diff --git a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
index 7f21b7a0..a137bb9c 100644
--- a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
+++ b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
@@ -4,6 +4,7 @@
 import life.mosu.mosuserver.domain.user.entity.UserJpaEntity;
 import life.mosu.mosuserver.domain.user.entity.UserRole;
 import life.mosu.mosuserver.domain.user.repository.UserJpaRepository;
+import life.mosu.mosuserver.global.exception.OAuthException;
 import life.mosu.mosuserver.global.processor.StepProcessor;
 import life.mosu.mosuserver.global.util.PhoneNumberUtil;
 import lombok.RequiredArgsConstructor;
@@ -28,9 +29,9 @@ public UserJpaEntity process(final OAuthUserInfo info) {
         return userRepository.findByPhoneNumber(
                         PhoneNumberUtil.formatPhoneNumber(info.phoneNumber()))
                 .map(existingUser -> {
-//                    if (existingUser.isMosuUser()) {
-//                        throw new IllegalArgumentException("이미 모수 회원입니다.");
-//                    }
+                    if (existingUser.isMosuUser()) {
+                        throw new OAuthException("DUPLICATE");
+                    }
                     existingUser.updateOAuthUser(
                             info.gender(),
                             info.name(),
diff --git a/src/main/java/life/mosu/mosuserver/global/exception/OAuthException.java b/src/main/java/life/mosu/mosuserver/global/exception/OAuthException.java
new file mode 100644
index 00000000..3a831272
--- /dev/null
+++ b/src/main/java/life/mosu/mosuserver/global/exception/OAuthException.java
@@ -0,0 +1,10 @@
+package life.mosu.mosuserver.global.exception;
+
+import org.springframework.security.core.AuthenticationException;
+
+public class OAuthException extends AuthenticationException {
+
+    public OAuthException(String msg) {
+        super(msg);
+    }
+}
diff --git a/src/main/java/life/mosu/mosuserver/global/handler/OAuth2LoginFailureHandler.java b/src/main/java/life/mosu/mosuserver/global/handler/OAuth2LoginFailureHandler.java
index cee9925a..f047a66b 100644
--- a/src/main/java/life/mosu/mosuserver/global/handler/OAuth2LoginFailureHandler.java
+++ b/src/main/java/life/mosu/mosuserver/global/handler/OAuth2LoginFailureHandler.java
@@ -6,7 +6,6 @@
 import jakarta.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
-import life.mosu.mosuserver.presentation.auth.dto.request.LoginResponse;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.security.core.AuthenticationException;
@@ -27,8 +26,11 @@ public class OAuth2LoginFailureHandler implements
     public void onAuthenticationFailure(HttpServletRequest request, HttpServletResponse response,
             AuthenticationException exception) throws IOException, ServletException {
 
-        LoginResponse loginResponse = LoginResponse.from();
-        String jsonResponse = UriUtils.encode(objectMapper.writeValueAsString(loginResponse),
+        OAuthErrorType errorType = OAuthErrorType.from(exception.getMessage());
+        OAuthFailureResponse oAuthFailureResponse = OAuthFailureResponse.from(
+                errorType.getMessage());
+
+        String jsonResponse = UriUtils.encode(objectMapper.writeValueAsString(oAuthFailureResponse),
                 StandardCharsets.UTF_8);
 
         final String redirectWithAccessToken = UriComponentsBuilder.fromUriString(
diff --git a/src/main/java/life/mosu/mosuserver/global/handler/OAuthErrorType.java b/src/main/java/life/mosu/mosuserver/global/handler/OAuthErrorType.java
new file mode 100644
index 00000000..9ae0e07a
--- /dev/null
+++ b/src/main/java/life/mosu/mosuserver/global/handler/OAuthErrorType.java
@@ -0,0 +1,27 @@
+package life.mosu.mosuserver.global.handler;
+
+import lombok.Getter;
+
+@Getter
+public enum OAuthErrorType {
+    CANCELED("CANCELED"),
+    DUPLICATE("DUPLICATE"),
+    UNKNOWN("UNKNOWN");
+
+    private final String message;
+
+    OAuthErrorType(String message) {
+        this.message = message;
+    }
+
+    public static OAuthErrorType from(String text) {
+        if (text == null) {
+            return UNKNOWN;
+        }
+        return switch (text) {
+            case "DUPLICATE" -> DUPLICATE;
+            case "[access_denied] User denied access" -> CANCELED;
+            default -> UNKNOWN;
+        };
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/life/mosu/mosuserver/global/handler/OAuthFailureResponse.java b/src/main/java/life/mosu/mosuserver/global/handler/OAuthFailureResponse.java
new file mode 100644
index 00000000..7af100e0
--- /dev/null
+++ b/src/main/java/life/mosu/mosuserver/global/handler/OAuthFailureResponse.java
@@ -0,0 +1,11 @@
+package life.mosu.mosuserver.global.handler;
+
+public record OAuthFailureResponse(
+        Boolean isProfileRegistered,
+        String errorCode
+) {
+
+    public static OAuthFailureResponse from(String errorCode) {
+        return new OAuthFailureResponse(null, errorCode);
+    }
+}
diff --git a/src/main/java/life/mosu/mosuserver/presentation/auth/dto/request/LoginResponse.java b/src/main/java/life/mosu/mosuserver/presentation/auth/dto/request/LoginResponse.java
index 7f206fe4..4f9f35ef 100644
--- a/src/main/java/life/mosu/mosuserver/presentation/auth/dto/request/LoginResponse.java
+++ b/src/main/java/life/mosu/mosuserver/presentation/auth/dto/request/LoginResponse.java
@@ -21,8 +21,4 @@ public static LoginResponse from(Boolean isProfileRegistered, final UserJpaEntit
         }
         return new LoginResponse(false, LoginUserResponse.from(user));
     }
-
-    public static LoginResponse from() {
-        return new LoginResponse(null, null);
-    }
 }