diff --git a/src/google/adk/tools/mcp_tool/mcp_session_manager.py b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
index 560c0b9..abc49da 100644
--- a/src/google/adk/tools/mcp_tool/mcp_session_manager.py
+++ b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
@@ -138,15 +138,15 @@ class MCPSessionManager:
         errlog: (Optional) TextIO stream for error logging. Use only for
           initializing a local stdio MCP session.
     """
-    self.connection_params = connection_params
-    self.exit_stack = exit_stack
-    self.errlog = errlog
+    self._connection_params = connection_params
+    self._exit_stack = exit_stack
+    self._errlog = errlog
 
   async def create_session(self) -> ClientSession:
     return await MCPSessionManager.initialize_session(
-        connection_params=self.connection_params,
-        exit_stack=self.exit_stack,
-        errlog=self.errlog,
+        connection_params=self._connection_params,
+        exit_stack=self._exit_stack,
+        errlog=self._errlog,
     )
 
   @classmethod
diff --git a/src/google/adk/tools/mcp_tool/mcp_tool.py b/src/google/adk/tools/mcp_tool/mcp_tool.py
index fc783d4..11ff5eb 100644
--- a/src/google/adk/tools/mcp_tool/mcp_tool.py
+++ b/src/google/adk/tools/mcp_tool/mcp_tool.py
@@ -81,15 +81,15 @@ class MCPTool(BaseTool):
       raise ValueError("mcp_session cannot be None")
     self.name = mcp_tool.name
     self.description = mcp_tool.description if mcp_tool.description else ""
-    self.mcp_tool = mcp_tool
-    self.mcp_session = mcp_session
-    self.mcp_session_manager = mcp_session_manager
+    self._mcp_tool = mcp_tool
+    self._mcp_session = mcp_session
+    self._mcp_session_manager = mcp_session_manager
     # TODO(cheliu): Support passing auth to MCP Server.
-    self.auth_scheme = auth_scheme
-    self.auth_credential = auth_credential
+    self._auth_scheme = auth_scheme
+    self._auth_credential = auth_credential
 
   async def _reinitialize_session(self):
-    self.mcp_session = await self.mcp_session_manager.create_session()
+    self._mcp_session = await self._mcp_session_manager.create_session()
 
   @override
   def _get_declaration(self) -> FunctionDeclaration:
@@ -98,7 +98,7 @@ class MCPTool(BaseTool):
     Returns:
         FunctionDeclaration: The Gemini function declaration for the tool.
     """
-    schema_dict = self.mcp_tool.inputSchema
+    schema_dict = self._mcp_tool.inputSchema
     parameters = to_gemini_schema(schema_dict)
     function_decl = FunctionDeclaration(
         name=self.name, description=self.description, parameters=parameters
@@ -119,7 +119,7 @@ class MCPTool(BaseTool):
     """
     # TODO(cheliu): Support passing tool context to MCP Server.
     try:
-      response = await self.mcp_session.call_tool(self.name, arguments=args)
+      response = await self._mcp_session.call_tool(self.name, arguments=args)
       return response
     except Exception as e:
       print(e)
diff --git a/src/google/adk/tools/mcp_tool/mcp_toolset.py b/src/google/adk/tools/mcp_tool/mcp_toolset.py
index 6cca5a0..e73ef6f 100644
--- a/src/google/adk/tools/mcp_tool/mcp_toolset.py
+++ b/src/google/adk/tools/mcp_tool/mcp_toolset.py
@@ -76,26 +76,28 @@ class MCPToolset(BaseToolset):
       connection_params: The connection parameters to the MCP server. Can be:
         `StdioServerParameters` for using local mcp server (e.g. using `npx` or
         `python3`); or `SseServerParams` for a local/remote SSE server.
+      errlog: (Optional) TextIO stream for error logging. Use only for
+        initializing a local stdio MCP session.
     """
 
     if not connection_params:
       raise ValueError('Missing connection params in MCPToolset.')
-    self.connection_params = connection_params
-    self.errlog = errlog
-    self.exit_stack = AsyncExitStack()
+    self._connection_params = connection_params
+    self._errlog = errlog
+    self._exit_stack = AsyncExitStack()
 
-    self.session_manager = MCPSessionManager(
-        connection_params=self.connection_params,
-        exit_stack=self.exit_stack,
-        errlog=self.errlog,
+    self._session_manager = MCPSessionManager(
+        connection_params=self._connection_params,
+        exit_stack=self._exit_stack,
+        errlogger=self._errlog,
     )
-    self.session = None
+    self._session = None
     self.tool_filter = tool_filter
 
   async def _initialize(self) -> ClientSession:
     """Connects to the MCP Server and initializes the ClientSession."""
-    self.session = await self.session_manager.create_session()
-    return self.session
+    self._session = await self._session_manager.create_session()
+    return self._session
 
   def _is_selected(
       self, tool: ..., readonly_context: Optional[ReadonlyContext]
@@ -112,7 +114,7 @@ class MCPToolset(BaseToolset):
   @override
   async def close(self):
     """Closes the connection to MCP Server."""
-    await self.exit_stack.aclose()
+    await self._exit_stack.aclose()
 
   @retry_on_closed_resource('_initialize')
   @override
@@ -125,14 +127,14 @@ class MCPToolset(BaseToolset):
     Returns:
       A list of MCPTools imported from the MCP Server.
     """
-    if not self.session:
+    if not self._session:
       await self._initialize()
-    tools_response: ListToolsResult = await self.session.list_tools()
+    tools_response: ListToolsResult = await self._session.list_tools()
     return [
         MCPTool(
             mcp_tool=tool,
-            mcp_session=self.session,
-            mcp_session_manager=self.session_manager,
+            mcp_session=self._session,
+            mcp_session_manager=self._session_manager,
         )
         for tool in tools_response.tools
         if self._is_selected(tool, readonly_context)