diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 47e313a..872e181 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
 
       - name: Install dependencies
         run: |
-          pip install pytest pytest-cov mysql-connector-python Pympler
+          pip install pytest pytest-cov mysql-connector-python Pympler orjson
 
       - name: Set up MySQL client
         run: sudo apt-get install mysql-client
diff --git a/mybatis/cache.py b/mybatis/cache.py
index 7962b4c..5f140ec 100644
--- a/mybatis/cache.py
+++ b/mybatis/cache.py
@@ -1,5 +1,4 @@
-import json
-import pickle
+import orjson as json
 import time
 from typing import Dict, Any, Optional
 
diff --git a/setup.py b/setup.py
index 7bc8187..e242437 100644
--- a/setup.py
+++ b/setup.py
@@ -12,7 +12,8 @@
     packages=find_packages(),
     install_requires=[
         'mysql-connector-python>=9.0.0',
-        'Pympler>=1.1'
+        'Pympler>=1.1',
+        'orjson>=3.10.12'
     ],
     classifiers=[
         'Programming Language :: Python :: 3',
diff --git a/test/test_cache.py b/test/test_cache.py
index c9c5986..8e4df2d 100644
--- a/test/test_cache.py
+++ b/test/test_cache.py
@@ -4,12 +4,14 @@
 from mybatis import Cache, CacheKey
 
 def test_basic():
-    cache = Cache(memory_limit=555, max_live_ms=10*1000)  # 50MB, 10sec
+    cache = Cache(memory_limit=400, max_live_ms=10*1000)  # 50MB, 10sec
     cache.put(CacheKey("a", [1, 'a', None]), [{"a1": 1}, {"a2": 2}])
     cache.put(CacheKey("b", [2, 'b', None]), "2")
     cache.put(CacheKey("c", [3, 'c', None]), "3")
     cache.put(CacheKey("d", [4, 'd', None]), None)
 
+    print ("============> memory_used:", cache.memory_used)
+
     assert cache.get(CacheKey('a', [1, 'a', None])) == None
     assert cache.get(CacheKey('b', [2, 'b', None])) == '2'
 
@@ -18,13 +20,13 @@ def test_basic():
         l.append((key, value, memory_usage, type(value)))
 
     assert len(l) == 3
-    assert l[0][0] == '{"sql": "b", "param_list": [2, "b", null]}'
+    assert l[0][0] == b'{"sql":"b","param_list":[2,"b",null]}'
     assert l[0][1] == '2'
 
-    assert l[1][0] == '{"sql": "d", "param_list": [4, "d", null]}'
+    assert l[1][0] == b'{"sql":"d","param_list":[4,"d",null]}'
     assert l[1][1] == None
 
-    assert l[2][0] == '{"sql": "c", "param_list": [3, "c", null]}'
+    assert l[2][0] == b'{"sql":"c","param_list":[3,"c",null]}'
     assert l[2][1] == '3'
 
     cache.put(CacheKey("e", [5, 'e', None]), "5")
@@ -36,17 +38,17 @@ def test_basic():
 
     assert len(l) == 3
 
-    assert l[0][0] == '{"sql": "e", "param_list": [5, "e", null]}'
+    assert l[0][0] == b'{"sql":"e","param_list":[5,"e",null]}'
     assert l[0][1] == '5'
 
-    assert l[1][0] == '{"sql": "b", "param_list": [2, "b", null]}'
+    assert l[1][0] == b'{"sql":"b","param_list":[2,"b",null]}'
     assert l[1][1] == '2'
 
-    assert l[2][0] == '{"sql": "d", "param_list": [4, "d", null]}'
+    assert l[2][0] == b'{"sql":"d","param_list":[4,"d",null]}'
     assert l[2][1] == None
 
 def test_timeout():
-    cache = Cache(memory_limit=555, max_live_ms=1 * 1000)  # 50MB, 10sec
+    cache = Cache(memory_limit=400, max_live_ms=1 * 1000)  # 50MB, 10sec
     cache.put(CacheKey("a", [1, 'a', None]), [{"a1": 1}, {"a2": 2}])
     cache.put(CacheKey("b", [2, 'b', None]), "2")
     cache.put(CacheKey("c", [3, 'c', None]), "3")
@@ -61,7 +63,7 @@ def test_timeout():
     assert cache.memory_used == 0
 
 def test_overwrite():
-    cache = Cache(memory_limit=180, max_live_ms=10 * 1000)  # 50MB, 10sec
+    cache = Cache(memory_limit=120, max_live_ms=10 * 1000)  # 50MB, 10sec
     cache.put(CacheKey("a", [1, 'a', None]), [{"a1": 1}, {"a2": 2}])
     #print ("++++>cache.memory_used:", cache.memory_used)
     cache.put(CacheKey("a", [1, 'a', None]), [{"a1": 1}, {"a2": 2}, {"a3":3}])