diff --git a/apps/backend/apps/admin/src/contest/contest.resolver.ts b/apps/backend/apps/admin/src/contest/contest.resolver.ts
index 8db19415fe..7a1c48d016 100644
--- a/apps/backend/apps/admin/src/contest/contest.resolver.ts
+++ b/apps/backend/apps/admin/src/contest/contest.resolver.ts
@@ -2,10 +2,8 @@ import { ParseBoolPipe } from '@nestjs/common'
 import { Args, Context, Int, Mutation, Query, Resolver } from '@nestjs/graphql'
 import { Contest, ContestProblem } from '@generated'
 import { AuthenticatedRequest, UseRolesGuard } from '@libs/auth'
-import { OPEN_SPACE_ID } from '@libs/constants'
 import {
   CursorValidationPipe,
-  GroupIDPipe,
   IDValidationPipe,
   RequiredIntPipe
 } from '@libs/pipe'
@@ -33,16 +31,10 @@ export class ContestResolver {
       new RequiredIntPipe('take')
     )
     take: number,
-    @Args(
-      'groupId',
-      { defaultValue: OPEN_SPACE_ID, type: () => Int },
-      GroupIDPipe
-    )
-    groupId: number,
     @Args('cursor', { nullable: true, type: () => Int }, CursorValidationPipe)
     cursor: number | null
   ) {
-    return await this.contestService.getContests(take, groupId, cursor)
+    return await this.contestService.getContests(take, cursor)
   }
 
   @Query(() => ContestWithParticipants)
@@ -56,35 +48,25 @@ export class ContestResolver {
   @Mutation(() => Contest)
   async createContest(
     @Args('input') input: CreateContestInput,
-    @Args(
-      'groupId',
-      { defaultValue: OPEN_SPACE_ID, type: () => Int },
-      GroupIDPipe
-    )
-    groupId: number,
     @Context('req') req: AuthenticatedRequest
   ) {
-    return await this.contestService.createContest(groupId, req.user.id, input)
+    return await this.contestService.createContest(req.user.id, input)
   }
 
   @Mutation(() => Contest)
-  async updateContest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
-    @Args('input') input: UpdateContestInput
-  ) {
-    return await this.contestService.updateContest(groupId, input)
+  async updateContest(@Args('input') input: UpdateContestInput) {
+    return await this.contestService.updateContest(input)
   }
 
   @Mutation(() => Contest)
   async deleteContest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
     @Args('contestId', { type: () => Int }) contestId: number
   ) {
-    return await this.contestService.deleteContest(groupId, contestId)
+    return await this.contestService.deleteContest(contestId)
   }
 
   /**
-   * Contest의 소속 Group을 Open Space(groupId === 1)로 이동시키기 위한 요청(Publicizing Requests)들을 불러옵니다.
+   * Contest를 공개(Open Space)로 이동시키기 위한 요청(Publicizing Requests)들을 불러옵니다.
    * @returns Publicizing Request 배열
    */
   @Query(() => [PublicizingRequest])
@@ -94,24 +76,19 @@ export class ContestResolver {
   }
 
   /**
-   * Contest의 소속 Group을 Open Space(groupId === 1)로 이동시키기 위한 요청(Publicizing Request)를 생성합니다.
-   * @param groupId Contest가 속한 Group의 ID. 이미 Open Space(groupId === 1)이 아니어야 합니다.
+   * Contest를 공개(Open Space)로 이동시키기 위한 요청(Publicizing Request)을 생성합니다.
    * @param contestId Contest의 ID
    * @returns 생성된 Publicizing Request
    */
   @Mutation(() => PublicizingRequest)
   async createPublicizingRequest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
     @Args('contestId', { type: () => Int }) contestId: number
   ) {
-    return await this.contestService.createPublicizingRequest(
-      groupId,
-      contestId
-    )
+    return await this.contestService.createPublicizingRequest(contestId)
   }
 
   /**
-   * Contest의 소속 Group을 Open Space(groupId === 1)로 이동시키기 위한 요청(Publicizing Request)을 처리합니다.
+   * Contest를 공개(Open Space)로 이동시키기 위한 요청(Publicizing Request)을 처리합니다.
    * @param contestId Publicizing Request를 생성한 contest의 Id
    * @param isAccepted 요청 수락 여부
    * @returns
@@ -130,13 +107,11 @@ export class ContestResolver {
 
   @Mutation(() => [ContestProblem])
   async importProblemsToContest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
     @Args('contestId', { type: () => Int }) contestId: number,
     @Args('problemIdsWithScore', { type: () => [ProblemScoreInput] })
     problemIdsWithScore: ProblemScoreInput[]
   ) {
     return await this.contestService.importProblemsToContest(
-      groupId,
       contestId,
       problemIdsWithScore
     )
@@ -144,13 +119,11 @@ export class ContestResolver {
 
   @Mutation(() => [ContestProblem])
   async removeProblemsFromContest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
     @Args('contestId', { type: () => Int })
     contestId: number,
     @Args('problemIds', { type: () => [Int] }) problemIds: number[]
   ) {
     return await this.contestService.removeProblemsFromContest(
-      groupId,
       contestId,
       problemIds
     )
@@ -188,16 +161,11 @@ export class ContestResolver {
 
   @Mutation(() => DuplicatedContestResponse)
   async duplicateContest(
-    @Args('groupId', { type: () => Int }, GroupIDPipe) groupId: number,
     @Args('contestId', { type: () => Int })
     contestId: number,
     @Context('req') req: AuthenticatedRequest
   ) {
-    return await this.contestService.duplicateContest(
-      groupId,
-      contestId,
-      req.user.id
-    )
+    return await this.contestService.duplicateContest(contestId, req.user.id)
   }
 
   /**
diff --git a/apps/backend/apps/admin/src/contest/contest.service.spec.ts b/apps/backend/apps/admin/src/contest/contest.service.spec.ts
index 6b92bc7f3d..4f213e14fb 100644
--- a/apps/backend/apps/admin/src/contest/contest.service.spec.ts
+++ b/apps/backend/apps/admin/src/contest/contest.service.spec.ts
@@ -1,6 +1,6 @@
 import { CACHE_MANAGER } from '@nestjs/cache-manager'
 import { Test, type TestingModule } from '@nestjs/testing'
-import { ContestProblem, Group, ContestRecord } from '@generated'
+import { ContestProblem, ContestRecord } from '@generated'
 import { Problem } from '@generated'
 import { Contest } from '@generated'
 import { faker } from '@faker-js/faker'
@@ -20,7 +20,6 @@ import type { PublicizingRequest } from './model/publicizing-request.model'
 
 const contestId = 1
 const userId = 1
-const groupId = 1
 const problemId = 2
 const startTime = faker.date.past()
 const endTime = faker.date.future()
@@ -36,7 +35,6 @@ const problemIdsWithScore = {
 const contest: Contest = {
   id: contestId,
   createdById: userId,
-  groupId,
   title: 'title',
   description: 'description',
   penalty: 20,
@@ -63,7 +61,6 @@ const contest: Contest = {
 const contestWithCount = {
   id: contestId,
   createdById: userId,
-  groupId,
   title: 'title',
   description: 'description',
   penalty: 20,
@@ -93,7 +90,6 @@ const contestWithCount = {
 const contestWithParticipants: ContestWithParticipants = {
   id: contestId,
   createdById: userId,
-  groupId,
   title: 'title',
   description: 'description',
   penalty: 20,
@@ -118,20 +114,6 @@ const contestWithParticipants: ContestWithParticipants = {
   benefits: 'benefits'
 }
 
-const group: Group = {
-  id: groupId,
-  groupName: 'groupName',
-  description: 'description',
-  config: {
-    showOnList: true,
-    allowJoinFromSearch: true,
-    allowJoinWithURL: false,
-    requireApprovalBeforeJoin: true
-  },
-  createTime: faker.date.past(),
-  updateTime: faker.date.past()
-}
-
 const problem: Problem = {
   id: problemId,
   createdById: 2,
@@ -257,9 +239,6 @@ const db = {
     updateMany: stub().resolves([Problem]),
     findFirstOrThrow: stub().resolves(Problem)
   },
-  group: {
-    findUnique: stub().resolves(Group)
-  },
   submission: {
     findMany: stub().resolves([submissionsWithProblemTitleAndUsername])
   },
@@ -310,7 +289,7 @@ describe('ContestService', () => {
     it('should return an array of contests', async () => {
       db.contest.findMany.resolves([contestWithCount])
 
-      const res = await service.getContests(5, 2, 0)
+      const res = await service.getContests(5, 0)
       expect(res).to.deep.equal([contestWithParticipants])
     })
   })
@@ -328,9 +307,8 @@ describe('ContestService', () => {
   describe('createContest', () => {
     it('should return created contest', async () => {
       db.contest.create.resolves(contest)
-      db.group.findUnique.resolves(group)
 
-      const res = await service.createContest(groupId, userId, input)
+      const res = await service.createContest(userId, input)
       expect(res).to.deep.equal(contest)
     })
   })
@@ -340,15 +318,9 @@ describe('ContestService', () => {
       db.contest.findFirst.resolves(contest)
       db.contest.update.resolves(contest)
 
-      const res = await service.updateContest(groupId, updateInput)
+      const res = await service.updateContest(updateInput)
       expect(res).to.deep.equal(contest)
     })
-
-    it('should throw error when groupId or contestId not exist', async () => {
-      expect(service.updateContest(1000, updateInput)).to.be.rejectedWith(
-        EntityNotExistException
-      )
-    })
   })
 
   describe('deleteContest', () => {
@@ -356,12 +328,12 @@ describe('ContestService', () => {
       db.contest.findFirst.resolves(contest)
       db.contest.delete.resolves(contest)
 
-      const res = await service.deleteContest(groupId, contestId)
+      const res = await service.deleteContest(contestId)
       expect(res).to.deep.equal(contest)
     })
 
-    it('should throw error when groupId or contestId not exist', async () => {
-      expect(service.deleteContest(1000, 1000)).to.be.rejectedWith(
+    it('should throw error when contestId not exist', async () => {
+      expect(service.deleteContest(1000)).to.be.rejectedWith(
         EntityNotExistException
       )
     })
@@ -381,7 +353,7 @@ describe('ContestService', () => {
       })
     })
 
-    it('should throw error when groupId or contestId not exist', async () => {
+    it('should throw error when contestId not exist', async () => {
       expect(service.handlePublicizingRequest(1000, true)).to.be.rejectedWith(
         EntityNotExistException
       )
@@ -407,9 +379,7 @@ describe('ContestService', () => {
       db.contestProblem.findFirst.resolves(null)
 
       const res = await Promise.all(
-        await service.importProblemsToContest(groupId, contestId, [
-          problemIdsWithScore
-        ])
+        await service.importProblemsToContest(contestId, [problemIdsWithScore])
       )
 
       expect(res).to.deep.equal([contestProblem])
@@ -420,7 +390,7 @@ describe('ContestService', () => {
       db.problem.update.resolves(problem)
       db.contestProblem.findFirst.resolves(ContestProblem)
 
-      const res = await service.importProblemsToContest(groupId, contestId, [
+      const res = await service.importProblemsToContest(contestId, [
         problemIdsWithScore
       ])
 
@@ -429,7 +399,7 @@ describe('ContestService', () => {
 
     it('should throw error when the contestId not exist', async () => {
       expect(
-        service.importProblemsToContest(groupId, 9999, [problemIdsWithScore])
+        service.importProblemsToContest(9999, [problemIdsWithScore])
       ).to.be.rejectedWith(EntityNotExistException)
     })
   })
diff --git a/apps/backend/apps/admin/src/contest/contest.service.ts b/apps/backend/apps/admin/src/contest/contest.service.ts
index d2a8ad0583..d95bca4205 100644
--- a/apps/backend/apps/admin/src/contest/contest.service.ts
+++ b/apps/backend/apps/admin/src/contest/contest.service.ts
@@ -1,14 +1,9 @@
 import { CACHE_MANAGER } from '@nestjs/cache-manager'
-import {
-  Inject,
-  Injectable,
-  UnprocessableEntityException
-} from '@nestjs/common'
+import { Inject, Injectable } from '@nestjs/common'
 import { Contest, ResultStatus, Submission } from '@generated'
 import type { ContestProblem } from '@prisma/client'
 import { Cache } from 'cache-manager'
 import {
-  OPEN_SPACE_ID,
   PUBLICIZING_REQUEST_EXPIRE_TIME,
   PUBLICIZING_REQUEST_KEY,
   MIN_DATE,
@@ -34,12 +29,11 @@ export class ContestService {
     @Inject(CACHE_MANAGER) private readonly cacheManager: Cache
   ) {}
 
-  async getContests(take: number, groupId: number, cursor: number | null) {
+  async getContests(take: number, cursor: number | null) {
     const paginator = this.prisma.getPaginator(cursor)
 
     const contests = await this.prisma.contest.findMany({
       ...paginator,
-      where: { groupId },
       take,
       include: {
         // eslint-disable-next-line @typescript-eslint/naming-convention
@@ -84,7 +78,6 @@ export class ContestService {
   }
 
   async createContest(
-    groupId: number,
     userId: number,
     contest: CreateContestInput
   ): Promise<Contest> {
@@ -94,20 +87,10 @@ export class ContestService {
       )
     }
 
-    const group = await this.prisma.group.findUnique({
-      where: {
-        id: groupId
-      }
-    })
-    if (!group) {
-      throw new EntityNotExistException('Group')
-    }
-
     try {
       return await this.prisma.contest.create({
         data: {
           createdById: userId,
-          groupId,
           ...contest
         }
       })
@@ -116,14 +99,10 @@ export class ContestService {
     }
   }
 
-  async updateContest(
-    groupId: number,
-    contest: UpdateContestInput
-  ): Promise<Contest> {
+  async updateContest(contest: UpdateContestInput): Promise<Contest> {
     const contestFound = await this.prisma.contest.findFirst({
       where: {
-        id: contest.id,
-        groupId
+        id: contest.id
       },
       select: {
         startTime: true,
@@ -214,11 +193,10 @@ export class ContestService {
     }
   }
 
-  async deleteContest(groupId: number, contestId: number) {
+  async deleteContest(contestId: number) {
     const contest = await this.prisma.contest.findFirst({
       where: {
-        id: contestId,
-        groupId
+        id: contestId
       },
       select: {
         contestProblem: {
@@ -236,7 +214,7 @@ export class ContestService {
       (problem) => problem.problemId
     )
     if (problemIds.length) {
-      await this.removeProblemsFromContest(groupId, contestId, problemIds)
+      await this.removeProblemsFromContest(contestId, problemIds)
     }
 
     try {
@@ -299,9 +277,7 @@ export class ContestService {
           where: {
             id: contestId
           },
-          data: {
-            groupId: OPEN_SPACE_ID
-          }
+          data: {}
         })
       } catch (error) {
         throw new UnprocessableDataException(error.message)
@@ -314,17 +290,10 @@ export class ContestService {
     } as PublicizingResponse
   }
 
-  async createPublicizingRequest(groupId: number, contestId: number) {
-    if (groupId == OPEN_SPACE_ID) {
-      throw new UnprocessableEntityException(
-        'This contest is already publicized'
-      )
-    }
-
+  async createPublicizingRequest(contestId: number) {
     const contest = await this.prisma.contest.findFirst({
       where: {
-        id: contestId,
-        groupId
+        id: contestId
       }
     })
     if (!contest) {
@@ -360,14 +329,12 @@ export class ContestService {
   }
 
   async importProblemsToContest(
-    groupId: number,
     contestId: number,
     problemIdsWithScore: ProblemScoreInput[]
   ) {
     const contest = await this.prisma.contest.findUnique({
       where: {
-        id: contestId,
-        groupId
+        id: contestId
       },
       include: {
         submission: {
@@ -442,15 +409,10 @@ export class ContestService {
     return contestProblems
   }
 
-  async removeProblemsFromContest(
-    groupId: number,
-    contestId: number,
-    problemIds: number[]
-  ) {
+  async removeProblemsFromContest(contestId: number, problemIds: number[]) {
     const contest = await this.prisma.contest.findUnique({
       where: {
-        id: contestId,
-        groupId
+        id: contestId
       },
       include: {
         submission: {
@@ -608,18 +570,16 @@ export class ContestService {
   /**
    * Duplicate contest with contest problems and users who participated in the contest
    * Not copied: submission
-   * @param groupId group to duplicate contest
    * @param contestId contest to duplicate
    * @param userId user who tries to duplicates the contest
    * @returns
    */
-  async duplicateContest(groupId: number, contestId: number, userId: number) {
+  async duplicateContest(contestId: number, userId: number) {
     const [contestFound, contestProblemsFound, userContestRecords] =
       await Promise.all([
         this.prisma.contest.findFirst({
           where: {
-            id: contestId,
-            groupId
+            id: contestId
           }
         }),
         this.prisma.contestProblem.findMany({
@@ -658,7 +618,6 @@ export class ContestService {
               ...contestDataToCopy,
               title: 'Copy of ' + title,
               createdById: userId,
-              groupId,
               isVisible: newVisible
             }
           })
diff --git a/apps/backend/apps/admin/src/problem/mock/mock.ts b/apps/backend/apps/admin/src/problem/mock/mock.ts
index a39bd61adc..c0d644672e 100644
--- a/apps/backend/apps/admin/src/problem/mock/mock.ts
+++ b/apps/backend/apps/admin/src/problem/mock/mock.ts
@@ -375,7 +375,6 @@ export const exampleContest: Contest = {
   description: 'example',
   penalty: 20,
   lastPenalty: false,
-  groupId: 1,
   createdById: 1,
   isVisible: true,
   isRankVisible: true,
diff --git a/apps/backend/apps/admin/src/problem/problem.service.ts b/apps/backend/apps/admin/src/problem/problem.service.ts
index 0043ff1e55..9063536f5b 100644
--- a/apps/backend/apps/admin/src/problem/problem.service.ts
+++ b/apps/backend/apps/admin/src/problem/problem.service.ts
@@ -605,7 +605,7 @@ export class ProblemService {
     contestId: number
   ): Promise<Partial<ContestProblem>[]> {
     await this.prisma.contest.findFirstOrThrow({
-      where: { id: contestId, groupId }
+      where: { id: contestId }
     })
     const contestProblems = await this.prisma.contestProblem.findMany({
       where: { contestId }
@@ -619,7 +619,7 @@ export class ProblemService {
     problemIdsWithScore: ProblemScoreInput[]
   ): Promise<Partial<ContestProblem>[]> {
     await this.prisma.contest.findFirstOrThrow({
-      where: { id: contestId, groupId }
+      where: { id: contestId }
     })
 
     const queries = problemIdsWithScore.map((record) => {
@@ -644,7 +644,7 @@ export class ProblemService {
     orders: number[]
   ): Promise<Partial<ContestProblem>[]> {
     await this.prisma.contest.findFirstOrThrow({
-      where: { id: contestId, groupId }
+      where: { id: contestId }
     })
 
     const contestProblems = await this.prisma.contestProblem.findMany({
diff --git a/apps/backend/apps/client/src/announcement/announcement.controller.ts b/apps/backend/apps/client/src/announcement/announcement.controller.ts
index 82038e4885..9bf96ba0dc 100644
--- a/apps/backend/apps/client/src/announcement/announcement.controller.ts
+++ b/apps/backend/apps/client/src/announcement/announcement.controller.ts
@@ -44,8 +44,7 @@ export class AnnouncementController {
       } else {
         if (contestId) {
           return await this.announcementService.getContestAnnouncements(
-            contestId,
-            groupId
+            contestId
           )
         } else {
           return await this.announcementService.getAssignmentAnnouncements(
diff --git a/apps/backend/apps/client/src/announcement/announcement.service.spec.ts b/apps/backend/apps/client/src/announcement/announcement.service.spec.ts
index be12cf43fb..7c0102f1c6 100644
--- a/apps/backend/apps/client/src/announcement/announcement.service.spec.ts
+++ b/apps/backend/apps/client/src/announcement/announcement.service.spec.ts
@@ -70,7 +70,7 @@ describe('AnnouncementService', () => {
 
   describe('getContestAnnouncements', () => {
     it('should return multiple contest announcements', async () => {
-      const res = await service.getContestAnnouncements(1, 1)
+      const res = await service.getContestAnnouncements(1)
       expect(res)
         .excluding(['createTime', 'updateTime', 'content'])
         .to.deep.equal([
diff --git a/apps/backend/apps/client/src/announcement/announcement.service.ts b/apps/backend/apps/client/src/announcement/announcement.service.ts
index 3f4818c707..679c8c3e1c 100644
--- a/apps/backend/apps/client/src/announcement/announcement.service.ts
+++ b/apps/backend/apps/client/src/announcement/announcement.service.ts
@@ -6,15 +6,11 @@ import { PrismaService } from '@libs/prisma'
 export class AnnouncementService {
   constructor(private readonly prisma: PrismaService) {}
 
-  async getContestAnnouncements(
-    contestId: number,
-    groupId: number
-  ): Promise<Announcement[]> {
+  async getContestAnnouncements(contestId: number): Promise<Announcement[]> {
     const { contestProblem, announcement } =
       await this.prisma.contest.findUniqueOrThrow({
         where: {
-          id: contestId,
-          groupId
+          id: contestId
         },
         select: {
           contestProblem: true,
@@ -73,8 +69,7 @@ export class AnnouncementService {
         where: {
           problemId,
           contest: {
-            id: contestId,
-            groupId
+            id: contestId
           }
         },
         orderBy: { updateTime: 'desc' }
diff --git a/apps/backend/apps/client/src/contest/contest.controller.ts b/apps/backend/apps/client/src/contest/contest.controller.ts
index b6c1e55ff4..c457b9614f 100644
--- a/apps/backend/apps/client/src/contest/contest.controller.ts
+++ b/apps/backend/apps/client/src/contest/contest.controller.ts
@@ -12,7 +12,7 @@ import {
   AuthNotNeededIfOpenSpace,
   UserNullWhenAuthFailedIfOpenSpace
 } from '@libs/auth'
-import { GroupIDPipe, IDValidationPipe, RequiredIntPipe } from '@libs/pipe'
+import { IDValidationPipe, RequiredIntPipe } from '@libs/pipe'
 import { ContestService } from './contest.service'
 
 @Controller('contest')
@@ -37,24 +37,21 @@ export class ContestController {
   @UserNullWhenAuthFailedIfOpenSpace()
   async getContest(
     @Req() req: AuthenticatedRequest,
-    @Query('groupId', GroupIDPipe) groupId: number,
     @Param('id', new RequiredIntPipe('id')) id: number
   ) {
-    return await this.contestService.getContest(id, groupId, req.user?.id)
+    return await this.contestService.getContest(id, req.user?.id)
   }
 
   @Post(':id/participation')
   async createContestRecord(
     @Req() req: AuthenticatedRequest,
-    @Query('groupId', GroupIDPipe) groupId: number,
     @Param('id', IDValidationPipe) contestId: number,
     @Query('invitationCode') invitationCode?: string
   ) {
     return await this.contestService.createContestRecord({
       contestId,
       userId: req.user.id,
-      invitationCode,
-      groupId
+      invitationCode
     })
   }
 
@@ -62,14 +59,9 @@ export class ContestController {
   @Delete(':id/participation')
   async deleteContestRecord(
     @Req() req: AuthenticatedRequest,
-    @Query('groupId', GroupIDPipe) groupId: number,
     @Param('id', IDValidationPipe) contestId: number
   ) {
-    return await this.contestService.deleteContestRecord(
-      contestId,
-      req.user.id,
-      groupId
-    )
+    return await this.contestService.deleteContestRecord(contestId, req.user.id)
   }
 
   @Get(':id/leaderboard')
diff --git a/apps/backend/apps/client/src/contest/contest.service.spec.ts b/apps/backend/apps/client/src/contest/contest.service.spec.ts
index bd14c24e98..213ba0473f 100644
--- a/apps/backend/apps/client/src/contest/contest.service.spec.ts
+++ b/apps/backend/apps/client/src/contest/contest.service.spec.ts
@@ -1,12 +1,7 @@
 import { CACHE_MANAGER } from '@nestjs/cache-manager'
 import { ConfigService } from '@nestjs/config'
 import { Test, type TestingModule } from '@nestjs/testing'
-import {
-  Prisma,
-  type Contest,
-  type Group,
-  type ContestRecord
-} from '@prisma/client'
+import { Prisma, type Contest, type ContestRecord } from '@prisma/client'
 import { expect } from 'chai'
 import * as dayjs from 'dayjs'
 import {
@@ -23,14 +18,12 @@ import { ContestService, type ContestResult } from './contest.service'
 
 const contestId = 1
 const user01Id = 4
-const groupId = 1
 
 const now = dayjs()
 
 const contest = {
   id: contestId,
   createdById: 1,
-  groupId,
   title: 'title',
   description: 'description',
   penalty: 100,
@@ -44,10 +37,6 @@ const contest = {
   enableCopyPaste: true,
   createTime: now.add(-1, 'day').toDate(),
   updateTime: now.add(-1, 'day').toDate(),
-  group: {
-    id: groupId,
-    groupName: 'group'
-  },
   posterUrl: 'posterUrl',
   participationTarget: 'participationTarget',
   competitionMethod: 'competitionMethod',
@@ -55,14 +44,11 @@ const contest = {
   problemFormat: 'problemFormat',
   benefits: 'benefits',
   invitationCode: '123456'
-} satisfies Contest & {
-  group: Partial<Group>
-}
+} satisfies Contest
 
 const ongoingContests = [
   {
     id: contest.id,
-    group: contest.group,
     title: contest.title,
     posterUrl: contest.posterUrl,
     participationTarget: contest.participationTarget,
@@ -83,7 +69,6 @@ const ongoingContests = [
 const upcomingContests = [
   {
     id: contest.id + 6,
-    group: contest.group,
     title: contest.title,
     posterUrl: null,
     participationTarget: null,
@@ -104,7 +89,6 @@ const upcomingContests = [
 const finishedContests = [
   {
     id: contest.id + 1,
-    group: contest.group,
     title: contest.title,
     posterUrl: contest.posterUrl,
     participationTarget: contest.participationTarget,
@@ -122,12 +106,6 @@ const finishedContests = [
   }
 ] satisfies Partial<ContestResult>[]
 
-const contests = [
-  ...ongoingContests,
-  ...finishedContests,
-  ...upcomingContests
-] satisfies Partial<ContestResult>[]
-
 describe('ContestService', () => {
   let service: ContestService
   let prisma: PrismaTestService
@@ -183,7 +161,7 @@ describe('ContestService', () => {
     })
 
     it('a contest should contain following fields when userId is undefined', async () => {
-      const contests = await service.getContests(groupId)
+      const contests = await service.getContests()
       expect(contests.ongoing[0]).to.have.property('title')
       expect(contests.ongoing[0]).to.have.property('startTime')
       expect(contests.ongoing[0]).to.have.property('endTime')
@@ -223,13 +201,13 @@ describe('ContestService', () => {
 
   describe('getContest', () => {
     it('should throw error when contest does not exist', async () => {
-      await expect(
-        service.getContest(999, groupId, user01Id)
-      ).to.be.rejectedWith(EntityNotExistException)
+      await expect(service.getContest(999, user01Id)).to.be.rejectedWith(
+        EntityNotExistException
+      )
     })
 
     it('should return contest', async () => {
-      expect(await service.getContest(contestId, groupId, user01Id)).to.be.ok
+      expect(await service.getContest(contestId, user01Id)).to.be.ok
     })
 
     it('should return optional fields if they exist', async () => {
@@ -242,7 +220,7 @@ describe('ContestService', () => {
     })
 
     it('should return prev and next contest information', async () => {
-      const contest = await service.getContest(contestId, groupId, user01Id)
+      const contest = await service.getContest(contestId, user01Id)
       if (contest.prev) {
         expect(contest.prev).to.have.property('id')
         expect(contest.prev.id).to.be.lessThan(contestId)
@@ -284,9 +262,9 @@ describe('ContestService', () => {
     it('should throw error when user is participated in contest again', async () => {
       await expect(
         service.createContestRecord({
-          contestId: contestId,
+          contestId,
           userId: user01Id,
-          invitationCode: invitationCode
+          invitationCode
         })
       ).to.be.rejectedWith(ConflictFoundException)
     })
@@ -296,7 +274,7 @@ describe('ContestService', () => {
         service.createContestRecord({
           contestId: 8,
           userId: user01Id,
-          invitationCode: invitationCode
+          invitationCode
         })
       ).to.be.rejectedWith(ConflictFoundException)
     })
@@ -305,7 +283,7 @@ describe('ContestService', () => {
       const contestRecord = await service.createContestRecord({
         contestId: 2,
         userId: user01Id,
-        invitationCode: invitationCode
+        invitationCode
       })
       contestRecordId = contestRecord.id
       expect(
diff --git a/apps/backend/apps/client/src/contest/contest.service.ts b/apps/backend/apps/client/src/contest/contest.service.ts
index bf8c512962..cd9783acd2 100644
--- a/apps/backend/apps/client/src/contest/contest.service.ts
+++ b/apps/backend/apps/client/src/contest/contest.service.ts
@@ -1,6 +1,5 @@
 import { Injectable } from '@nestjs/common'
 import { Prisma, Role, type Contest } from '@prisma/client'
-import { OPEN_SPACE_ID } from '@libs/constants'
 import {
   ConflictFoundException,
   EntityNotExistException,
@@ -13,7 +12,6 @@ const contestSelectOption = {
   title: true,
   startTime: true,
   endTime: true,
-  group: { select: { id: true, groupName: true } },
   contestRecord: {
     select: {
       userId: true
@@ -181,7 +179,7 @@ export class ContestService {
     }
   }
 
-  async getContest(id: number, groupId = OPEN_SPACE_ID, userId?: number) {
+  async getContest(id: number, userId?: number) {
     // check if the user has already registered this contest
     // initial value is false
     let isRegistered = false
@@ -198,7 +196,6 @@ export class ContestService {
       contest = await this.prisma.contest.findUniqueOrThrow({
         where: {
           id,
-          groupId,
           isVisible: true
         },
         select: {
@@ -263,7 +260,6 @@ export class ContestService {
       return {
         where: {
           id: options.compare,
-          groupId,
           isVisible: true
         },
         orderBy: {
@@ -288,20 +284,19 @@ export class ContestService {
   async createContestRecord({
     contestId,
     userId,
-    invitationCode,
-    groupId = OPEN_SPACE_ID
+    invitationCode
   }: {
     contestId: number
     userId: number
     invitationCode?: string
-    groupId?: number
   }) {
     const contest = await this.prisma.contest.findUniqueOrThrow({
-      where: { id: contestId, groupId },
+      where: {
+        id: contestId
+      },
       select: {
         startTime: true,
         endTime: true,
-        groupId: true,
         invitationCode: true
       }
     })
@@ -326,27 +321,27 @@ export class ContestService {
     })
   }
 
-  async isVisible(contestId: number, groupId: number): Promise<boolean> {
+  async isVisible(contestId: number): Promise<boolean> {
     return !!(await this.prisma.contest.count({
       where: {
         id: contestId,
-        isVisible: true,
-        groupId
+        isVisible: true
       }
     }))
   }
 
-  async deleteContestRecord(
-    contestId: number,
-    userId: number,
-    groupId = OPEN_SPACE_ID
-  ) {
+  async deleteContestRecord(contestId: number, userId: number) {
     const [contest, contestRecord] = await Promise.all([
       this.prisma.contest.findUnique({
-        where: { id: contestId, groupId }
+        where: {
+          id: contestId
+        }
       }),
       this.prisma.contestRecord.findFirst({
-        where: { userId, contestId }
+        where: {
+          userId,
+          contestId
+        }
       })
     ])
 
diff --git a/apps/backend/apps/client/src/problem/problem.service.ts b/apps/backend/apps/client/src/problem/problem.service.ts
index 2b135d7d73..da1650c756 100644
--- a/apps/backend/apps/client/src/problem/problem.service.ts
+++ b/apps/backend/apps/client/src/problem/problem.service.ts
@@ -284,11 +284,7 @@ export class ContestProblemService {
     take: number
     groupId: number
   }) {
-    const contest = await this.contestService.getContest(
-      contestId,
-      groupId,
-      userId
-    )
+    const contest = await this.contestService.getContest(contestId, userId)
     const now = new Date()
     if (contest.isRegistered && contest.startTime! > now) {
       throw new ForbiddenAccessException(
@@ -414,11 +410,7 @@ export class ContestProblemService {
     userId: number
     groupId: number
   }) {
-    const contest = await this.contestService.getContest(
-      contestId,
-      groupId,
-      userId
-    )
+    const contest = await this.contestService.getContest(contestId, userId)
     const now = new Date()
     if (contest.isRegistered) {
       if (now < contest.startTime!) {
diff --git a/apps/backend/apps/client/src/submission/submission.controller.ts b/apps/backend/apps/client/src/submission/submission.controller.ts
index a955b56ea8..70393dde86 100644
--- a/apps/backend/apps/client/src/submission/submission.controller.ts
+++ b/apps/backend/apps/client/src/submission/submission.controller.ts
@@ -67,8 +67,7 @@ export class SubmissionController {
         userIp,
         userId: req.user.id,
         problemId,
-        contestId,
-        groupId
+        contestId
       })
     } else if (assignmentId) {
       return await this.submissionService.submitToAssignment({
diff --git a/apps/backend/apps/client/src/submission/submission.service.ts b/apps/backend/apps/client/src/submission/submission.service.ts
index 2abd8dc7ca..178633fcbe 100644
--- a/apps/backend/apps/client/src/submission/submission.service.ts
+++ b/apps/backend/apps/client/src/submission/submission.service.ts
@@ -143,15 +143,13 @@ export class SubmissionService {
     userIp,
     userId,
     problemId,
-    contestId,
-    groupId = OPEN_SPACE_ID
+    contestId
   }: {
     submissionDto: CreateSubmissionDto
     userIp: string
     userId: number
     problemId: number
     contestId: number
-    groupId: number
   }) {
     const now = new Date()
 
@@ -159,7 +157,6 @@ export class SubmissionService {
     const contest = await this.prisma.contest.findFirst({
       where: {
         id: contestId,
-        groupId,
         startTime: {
           lte: now
         },
@@ -184,7 +181,6 @@ export class SubmissionService {
       select: {
         contest: {
           select: {
-            groupId: true,
             startTime: true,
             endTime: true
           }
@@ -194,9 +190,7 @@ export class SubmissionService {
     if (!contestRecord) {
       throw new EntityNotExistException('ContestRecord')
     }
-    if (contestRecord.contest.groupId !== groupId) {
-      throw new EntityNotExistException('Contest')
-    } else if (
+    if (
       contestRecord.contest.startTime > now ||
       contestRecord.contest.endTime <= now
     ) {
@@ -957,7 +951,6 @@ export class SubmissionService {
   }) {
     const now = new Date()
     let contest: {
-      groupId: number
       startTime: Date
       endTime: Date
       isJudgeResultVisible: boolean
@@ -982,7 +975,6 @@ export class SubmissionService {
         select: {
           contest: {
             select: {
-              groupId: true,
               startTime: true,
               endTime: true,
               isJudgeResultVisible: true
@@ -993,9 +985,6 @@ export class SubmissionService {
       if (!contestRecord) {
         throw new EntityNotExistException('ContestRecord')
       }
-      if (contestRecord.contest.groupId !== groupId) {
-        throw new EntityNotExistException('Contest')
-      }
       contest = contestRecord.contest
       isJudgeResultVisible = contest.isJudgeResultVisible
     } else if (assignmentId) {
diff --git a/apps/backend/apps/client/src/submission/test/submission.service.spec.ts b/apps/backend/apps/client/src/submission/test/submission.service.spec.ts
index 2a5e1d3158..591438724a 100644
--- a/apps/backend/apps/client/src/submission/test/submission.service.spec.ts
+++ b/apps/backend/apps/client/src/submission/test/submission.service.spec.ts
@@ -84,7 +84,6 @@ const WORKBOOK_ID = 1
 const mockContest: Contest = {
   id: CONTEST_ID,
   createdById: 1,
-  groupId: 1,
   title: 'SKKU Coding Platform 모의대회',
   description: 'test',
   penalty: 20,
@@ -246,8 +245,7 @@ describe('SubmissionService', () => {
         userIp: USERIP,
         userId: submissions[0].userId,
         problemId: problems[0].id,
-        contestId: CONTEST_ID,
-        groupId: problems[0].groupId
+        contestId: CONTEST_ID
       })
       expect(createSpy.calledOnce).to.be.true
     })
@@ -262,8 +260,7 @@ describe('SubmissionService', () => {
           userIp: USERIP,
           userId: submissions[0].userId,
           problemId: problems[0].id,
-          contestId: CONTEST_ID,
-          groupId: problems[0].groupId
+          contestId: CONTEST_ID
         })
       ).to.be.rejectedWith(EntityNotExistException)
       expect(createSpy.called).to.be.false
diff --git a/apps/backend/prisma/migrations/20250130102040_delete_group_from_contest/migration.sql b/apps/backend/prisma/migrations/20250130102040_delete_group_from_contest/migration.sql
new file mode 100644
index 0000000000..a80ac62fe1
--- /dev/null
+++ b/apps/backend/prisma/migrations/20250130102040_delete_group_from_contest/migration.sql
@@ -0,0 +1,11 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `group_id` on the `contest` table. All the data in the column will be lost.
+
+*/
+-- DropForeignKey
+ALTER TABLE "contest" DROP CONSTRAINT "contest_group_id_fkey";
+
+-- AlterTable
+ALTER TABLE "contest" DROP COLUMN "group_id";
diff --git a/apps/backend/prisma/schema.prisma b/apps/backend/prisma/schema.prisma
index 96814a6c2b..e8c59263a9 100644
--- a/apps/backend/prisma/schema.prisma
+++ b/apps/backend/prisma/schema.prisma
@@ -122,7 +122,6 @@ model Group {
   problem    Problem[]
   assignment Assignment[]
   workbook   Workbook[]
-  contest    Contest[]
 
   @@map("group")
 }
@@ -327,11 +326,9 @@ model AssignmentRecord {
 }
 
 model Contest {
-  id                   Int       @id @default(autoincrement())
-  createdBy            User?     @relation(fields: [createdById], references: [id], onDelete: SetNull)
-  createdById          Int?      @map("created_by_id")
-  group                Group     @relation(fields: [groupId], references: [id])
-  groupId              Int       @map("group_id")
+  id                   Int      @id @default(autoincrement())
+  createdBy            User?    @relation(fields: [createdById], references: [id], onDelete: SetNull)
+  createdById          Int?     @map("created_by_id")
   title                String
   description          String
   // 대회의 페널티 (0 ≤ penalty ≤ 100),
diff --git a/apps/backend/prisma/seed.ts b/apps/backend/prisma/seed.ts
index 09b1219c02..d277373470 100644
--- a/apps/backend/prisma/seed.ts
+++ b/apps/backend/prisma/seed.ts
@@ -958,7 +958,6 @@ const createContests = async () => {
       title: string
       description: string
       createdById: number
-      groupId: number
       posterUrl: string | null
       participationTarget: string | null
       competitionMethod: string | null
@@ -1008,7 +1007,6 @@ const createContests = async () => {
   아니하고는 처벌·보안처분 또는 강제노역을 받지 아니한다.
 </p>`,
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: `https://skkuding.dev/open-graph.png`,
         participationTarget: '성균관대 재학생이라면 누구나',
         competitionMethod: '온라인으로 진행',
@@ -1028,7 +1026,6 @@ const createContests = async () => {
         title: '24년도 소프트웨어학과 신입생 입학 테스트1',
         description: '<p>이 대회는 현재 진행 중입니다 !</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '성균관대학교 24학번 신입생',
         competitionMethod: '강의실에서 오프라인으로 진행',
@@ -1048,7 +1045,6 @@ const createContests = async () => {
         title: '24년도 소프트웨어학과 신입생 입학 테스트2',
         description: '<p>이 대회는 현재 진행 중입니다 !</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: `https://skkuding.dev/open-graph.png`,
         participationTarget: '성균관대학교 24학번 신입생',
         competitionMethod: '강의실에서 오프라인으로 진행',
@@ -1068,7 +1064,6 @@ const createContests = async () => {
         title: '24년도 소프트웨어학과 신입생 입학 테스트3',
         description: '<p>이 대회는 현재 진행 중입니다 !</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: `https://skkuding.dev/open-graph.png`,
         participationTarget: '성균관대학교 24학번 신입생',
         competitionMethod: '강의실에서 오프라인으로 진행',
@@ -1088,7 +1083,6 @@ const createContests = async () => {
         title: '24년도 아늑배 스파게티 코드 만들기 대회',
         description: '<p>이 대회는 현재 진행 중입니다 ! (private group)</p>',
         createdById: superAdminUser.id,
-        groupId: privateGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '삼성학술정보관 지하1층에서 오프라인 진행',
@@ -1109,7 +1103,6 @@ const createContests = async () => {
         title: 'Long Time Ago Assignment',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공생',
         competitionMethod: '온라인 진행',
@@ -1129,7 +1122,6 @@ const createContests = async () => {
         title: '23년도 소프트웨어학과 신입생 입학 테스트',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 23학번',
         competitionMethod: '온라인 진행',
@@ -1149,7 +1141,6 @@ const createContests = async () => {
         title: '소프트의 아침',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1169,7 +1160,6 @@ const createContests = async () => {
         title: '소프트의 낮',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1189,7 +1179,6 @@ const createContests = async () => {
         title: '소프트의 밤',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1209,7 +1198,6 @@ const createContests = async () => {
         title: '2023 SKKU 프로그래밍 대회',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1229,7 +1217,6 @@ const createContests = async () => {
         title: '소프트의 오전',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1249,7 +1236,6 @@ const createContests = async () => {
         title: '소프트의 오후',
         description: '<p>이 대회는 오래 전에 끝났어요</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1269,7 +1255,6 @@ const createContests = async () => {
         title: '23년도 아늑배 스파게티 코드 만들기 대회',
         description: '<p>이 대회는 오래 전에 끝났어요 (private group)</p>',
         createdById: superAdminUser.id,
-        groupId: privateGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행',
@@ -1290,7 +1275,6 @@ const createContests = async () => {
         title: 'Future Assignment',
         description: '<p>이 대회는 언젠가 열리겠죠...?</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행 예정...?',
@@ -1310,7 +1294,6 @@ const createContests = async () => {
         title: '2024 SKKU 프로그래밍 대회',
         description: '<p>이 대회는 언젠가 열리겠죠...?</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행 예정...?',
@@ -1331,7 +1314,6 @@ const createContests = async () => {
         description:
           '<p>이 대회는 언젠가 열리겠죠...? isVisible이 false인 assignment입니다</p>',
         createdById: superAdminUser.id,
-        groupId: publicGroup.id,
         posterUrl: `https://skkuding.dev/open-graph.png`,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행 예정...?',
@@ -1351,7 +1333,6 @@ const createContests = async () => {
         title: '25년도 아늑배 스파게티 코드 만들기 대회',
         description: '<p>이 대회는 언젠가 열리겠죠...? (private group)</p>',
         createdById: superAdminUser.id,
-        groupId: privateGroup.id,
         posterUrl: null,
         participationTarget: '소프트웨어학과 원전공/복수전공',
         competitionMethod: '온라인 진행 예정...?',
@@ -2396,39 +2377,58 @@ const createAssignmentRecords = async () => {
 
 const createContestRecords = async () => {
   const contestRecords: ContestRecord[] = []
-  // group 1 users
-  const group1Users = await prisma.userGroup.findMany({
-    where: {
-      groupId: 1
-    }
-  })
-  for (const user of group1Users) {
-    const contestRecord = await prisma.contestRecord.create({
-      data: {
-        userId: user.userId,
+  // all users
+  const users = await prisma.user.findMany()
+  for (const user of users) {
+    const existingRecord = await prisma.contestRecord.findFirst({
+      where: {
         contestId: 1,
-        acceptedProblemNum: 0,
-        totalPenalty: 0
+        userId: user.id
       }
     })
-    contestRecords.push(contestRecord)
-  }
-
-  // upcoming contest에 참가한 User 1의 contest register를 un-register하는 기능과,
-  // registered upcoming, ongoing, finished contest를 조회하는 기능을 확인하기 위함
-  const user01Id = 4
-  for (let contestId = 3; contestId <= contests.length; contestId += 2) {
-    contestRecords.push(
-      await prisma.contestRecord.create({
+    if (!existingRecord) {
+      const contestRecord = await prisma.contestRecord.create({
         data: {
-          userId: user01Id,
-          contestId,
+          userId: user.id,
+          contestId: 1,
           acceptedProblemNum: 0,
-          score: 0,
           totalPenalty: 0
         }
       })
-    )
+      contestRecords.push(contestRecord)
+    }
+  }
+
+  // upcoming contest에 참가한 User 1의 contest register를 un-register하는 기능과,
+  // registered upcoming, ongoing, finished contest를 조회하는 기능을 확인하기 위함
+  const contests = await prisma.contest.findMany({
+    select: {
+      id: true
+    }
+  })
+  const user01Id = 4
+  for (let i = 0; i < contests.length; i += 2) {
+    const contestId = contests[i].id
+    // eslint-disable-next-line @typescript-eslint/naming-convention
+    const existingRecord = await prisma.contestRecord.findFirst({
+      where: {
+        contestId: contestId,
+        userId: user01Id
+      }
+    })
+    if (!existingRecord) {
+      contestRecords.push(
+        await prisma.contestRecord.create({
+          data: {
+            userId: user01Id,
+            contestId,
+            acceptedProblemNum: 0,
+            score: 0,
+            totalPenalty: 0
+          }
+        })
+      )
+    }
   }
 
   return contestRecords