diff --git a/README.md b/README.md
index e7d935f..783db87 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,24 @@ filter.raw_query = {
 e.load_filtered_policy(filter)
 ```
 
+## Using an Existing MongoDB Client
+
+If you already have a MongoDB client instance in your application, you can reuse it:
+
+```python
+from pymongo import MongoClient
+import casbin_pymongo_adapter
+import casbin
+
+# Create or use your existing MongoDB client
+mongo_client = MongoClient('mongodb://localhost:27017/')
+
+# Pass the client to the adapter
+adapter = casbin_pymongo_adapter.Adapter(client=mongo_client, db_name="casbin")
+
+e = casbin.Enforcer('path/to/model.conf', adapter, True)
+```
+
 ## Async Example
 
 ```python
@@ -73,6 +91,23 @@ e = casbin.AsyncEnforcer('path/to/model.conf', adapter)
 await e.load_policy()
 ```
 
+### Using an Existing AsyncMongoClient
+
+```python
+from pymongo import AsyncMongoClient
+from casbin_pymongo_adapter.asynchronous import Adapter
+import casbin
+
+# Create or use your existing AsyncMongoClient
+mongo_client = AsyncMongoClient('mongodb://localhost:27017/')
+
+# Pass the client to the adapter
+adapter = Adapter(client=mongo_client, db_name="casbin")
+e = casbin.AsyncEnforcer('path/to/model.conf', adapter)
+
+await e.load_policy()
+```
+
 
 ### Getting Help
 
diff --git a/casbin_pymongo_adapter/adapter.py b/casbin_pymongo_adapter/adapter.py
index 9cb4beb..4e4d4c7 100644
--- a/casbin_pymongo_adapter/adapter.py
+++ b/casbin_pymongo_adapter/adapter.py
@@ -9,22 +9,47 @@ class Adapter(persist.Adapter):
 
     def __init__(
         self,
-        uri,
-        dbname,
+        uri=None,
+        dbname=None,
         collection="casbin_rule",
         filtered=False,
+        client=None,
+        db_name=None,
     ):
         """Create an adapter for Mongodb
 
         Args:
-            uri (str): This should be the same requiement as pymongo Client's 'uri' parameter.
+            uri (str, optional): This should be the same requiement as pymongo Client's 'uri' parameter.
                           See https://pymongo.readthedocs.io/en/stable/api/pymongo/mongo_client.html#pymongo.mongo_client.MongoClient.
-            dbname (str): Database to store policy.
+                          Required if client is not provided.
+            dbname (str, optional): Database to store policy. Required if client is not provided.
             collection (str, optional): Collection of the choosen database. Defaults to "casbin_rule".
             filtered (bool, optional): Whether to use filtered query. Defaults to False.
+            client (MongoClient, optional): An existing MongoClient instance to reuse. If provided, uri is ignored.
+            db_name (str, optional): Database name to use with the provided client. Takes precedence over dbname.
+
+        Note:
+            When both client and uri are provided, client takes precedence and uri is ignored.
         """
-        client = MongoClient(uri)
-        db = client[dbname]
+        # Support both db_name and dbname for backward compatibility
+        database_name = db_name if db_name is not None else dbname
+
+        if client is not None:
+            # Use the provided client
+            if database_name is None:
+                raise ValueError(
+                    "db_name or dbname must be provided when using an existing client"
+                )
+            mongo_client = client
+        else:
+            # Create a new client from URI
+            if uri is None:
+                raise ValueError("uri must be provided when client is not specified")
+            if database_name is None:
+                raise ValueError("dbname must be provided when client is not specified")
+            mongo_client = MongoClient(uri)
+
+        db = mongo_client[database_name]
         self._collection = db[collection]
         self._filtered = filtered
 
diff --git a/casbin_pymongo_adapter/asynchronous/adapter.py b/casbin_pymongo_adapter/asynchronous/adapter.py
index b124397..34e8501 100644
--- a/casbin_pymongo_adapter/asynchronous/adapter.py
+++ b/casbin_pymongo_adapter/asynchronous/adapter.py
@@ -10,22 +10,47 @@ class Adapter(AsyncAdapter):
 
     def __init__(
         self,
-        uri,
-        dbname,
+        uri=None,
+        dbname=None,
         collection="casbin_rule",
         filtered=False,
+        client=None,
+        db_name=None,
     ):
         """Create an adapter for Mongodb
 
         Args:
-            uri (str): This should be the same requiement as pymongo Client's 'uri' parameter.
+            uri (str, optional): This should be the same requiement as pymongo Client's 'uri' parameter.
                           See https://pymongo.readthedocs.io/en/stable/api/pymongo/mongo_client.html#pymongo.mongo_client.MongoClient.
-            dbname (str): Database to store policy.
+                          Required if client is not provided.
+            dbname (str, optional): Database to store policy. Required if client is not provided.
             collection (str, optional): Collection of the choosen database. Defaults to "casbin_rule".
             filtered (bool, optional): Whether to use filtered query. Defaults to False.
+            client (AsyncMongoClient, optional): An existing AsyncMongoClient instance to reuse. If provided, uri is ignored.
+            db_name (str, optional): Database name to use with the provided client. Takes precedence over dbname.
+
+        Note:
+            When both client and uri are provided, client takes precedence and uri is ignored.
         """
-        client = AsyncMongoClient(uri)
-        db = client[dbname]
+        # Support both db_name and dbname for backward compatibility
+        database_name = db_name if db_name is not None else dbname
+
+        if client is not None:
+            # Use the provided client
+            if database_name is None:
+                raise ValueError(
+                    "db_name or dbname must be provided when using an existing client"
+                )
+            mongo_client = client
+        else:
+            # Create a new client from URI
+            if uri is None:
+                raise ValueError("uri must be provided when client is not specified")
+            if database_name is None:
+                raise ValueError("dbname must be provided when client is not specified")
+            mongo_client = AsyncMongoClient(uri)
+
+        db = mongo_client[database_name]
         self._collection = db[collection]
         self._filtered = filtered