diff --git a/lightrag/kg/mongo_impl.py b/lightrag/kg/mongo_impl.py
index 6b249b94..cf4822e5 100644
--- a/lightrag/kg/mongo_impl.py
+++ b/lightrag/kg/mongo_impl.py
@@ -40,36 +40,39 @@ GRAPH_BFS_MODE = os.getenv("MONGO_GRAPH_BFS_MODE", "bidirectional")
 
 class ClientManager:
     _instances = {"db": None, "ref_count": 0}
+    _lock = asyncio.Lock()
 
     @classmethod
     async def get_client(cls) -> AsyncMongoClient:
-        if cls._instances["db"] is None:
-            uri = os.environ.get(
-                "MONGO_URI",
-                config.get(
-                    "mongodb",
-                    "uri",
-                    fallback="mongodb://root:root@localhost:27017/",
-                ),
-            )
-            database_name = os.environ.get(
-                "MONGO_DATABASE",
-                config.get("mongodb", "database", fallback="LightRAG"),
-            )
-            client = AsyncMongoClient(uri)
-            db = client.get_database(database_name)
-            cls._instances["db"] = db
-            cls._instances["ref_count"] = 0
-        cls._instances["ref_count"] += 1
-        return cls._instances["db"]
+        async with cls._lock:
+            if cls._instances["db"] is None:
+                uri = os.environ.get(
+                    "MONGO_URI",
+                    config.get(
+                        "mongodb",
+                        "uri",
+                        fallback="mongodb://root:root@localhost:27017/",
+                    ),
+                )
+                database_name = os.environ.get(
+                    "MONGO_DATABASE",
+                    config.get("mongodb", "database", fallback="LightRAG"),
+                )
+                client = AsyncMongoClient(uri)
+                db = client.get_database(database_name)
+                cls._instances["db"] = db
+                cls._instances["ref_count"] = 0
+            cls._instances["ref_count"] += 1
+            return cls._instances["db"]
 
     @classmethod
     async def release_client(cls, db: AsyncDatabase):
-        if db is not None:
-            if db is cls._instances["db"]:
-                cls._instances["ref_count"] -= 1
-                if cls._instances["ref_count"] == 0:
-                    cls._instances["db"] = None
+        async with cls._lock:
+            if db is not None:
+                if db is cls._instances["db"]:
+                    cls._instances["ref_count"] -= 1
+                    if cls._instances["ref_count"] == 0:
+                        cls._instances["db"] = None
 
 
 @final