diff --git a/pyproject.toml b/pyproject.toml
index a9e9f2b..436db8c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -147,3 +147,4 @@ line_length = 200
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 asyncio_default_fixture_loop_scope = "function"
+asyncio_mode = "auto"
diff --git a/src/google/adk/agents/llm_agent.py b/src/google/adk/agents/llm_agent.py
index a140997..67e2d31 100644
--- a/src/google/adk/agents/llm_agent.py
+++ b/src/google/adk/agents/llm_agent.py
@@ -15,12 +15,7 @@
 from __future__ import annotations
 
 import logging
-from typing import Any
-from typing import AsyncGenerator
-from typing import Callable
-from typing import Literal
-from typing import Optional
-from typing import Union
+from typing import Any, AsyncGenerator, Awaitable, Callable, Literal, Optional, Union
 
 from google.genai import types
 from pydantic import BaseModel
@@ -62,11 +57,11 @@ AfterModelCallback: TypeAlias = Callable[
 ]
 BeforeToolCallback: TypeAlias = Callable[
     [BaseTool, dict[str, Any], ToolContext],
-    Optional[dict],
+    Union[Awaitable[Optional[dict]], Optional[dict]],
 ]
 AfterToolCallback: TypeAlias = Callable[
     [BaseTool, dict[str, Any], ToolContext, dict],
-    Optional[dict],
+    Union[Awaitable[Optional[dict]], Optional[dict]],
 ]
 
 InstructionProvider: TypeAlias = Callable[[ReadonlyContext], str]
diff --git a/src/google/adk/flows/llm_flows/functions.py b/src/google/adk/flows/llm_flows/functions.py
index 7c5fcfb..0e728b5 100644
--- a/src/google/adk/flows/llm_flows/functions.py
+++ b/src/google/adk/flows/llm_flows/functions.py
@@ -151,28 +151,33 @@ async def handle_function_calls_async(
     # do not use "args" as the variable name, because it is a reserved keyword
     # in python debugger.
     function_args = function_call.args or {}
-    function_response = None
-    # Calls the tool if before_tool_callback does not exist or returns None.
+    function_response: Optional[dict] = None
+
+    # before_tool_callback (sync or async)
     if agent.before_tool_callback:
       function_response = agent.before_tool_callback(
           tool=tool, args=function_args, tool_context=tool_context
       )
+      if inspect.isawaitable(function_response):
+        function_response = await function_response
 
     if not function_response:
       function_response = await __call_tool_async(
           tool, args=function_args, tool_context=tool_context
       )
 
-    # Calls after_tool_callback if it exists.
+    # after_tool_callback (sync or async)
     if agent.after_tool_callback:
-      new_response = agent.after_tool_callback(
+      altered_function_response = agent.after_tool_callback(
           tool=tool,
           args=function_args,
           tool_context=tool_context,
           tool_response=function_response,
       )
-      if new_response:
-        function_response = new_response
+      if inspect.isawaitable(altered_function_response):
+        altered_function_response = await altered_function_response
+      if altered_function_response is not None:
+        function_response = altered_function_response
 
     if tool.is_long_running:
       # Allow long running function to return None to not provide function response.
@@ -223,11 +228,17 @@ async def handle_function_calls_live(
     # in python debugger.
     function_args = function_call.args or {}
     function_response = None
-    # Calls the tool if before_tool_callback does not exist or returns None.
+    # # Calls the tool if before_tool_callback does not exist or returns None.
+    # if agent.before_tool_callback:
+    #   function_response = agent.before_tool_callback(
+    #       tool, function_args, tool_context
+    #   )
     if agent.before_tool_callback:
       function_response = agent.before_tool_callback(
-          tool, function_args, tool_context
+          tool=tool, args=function_args, tool_context=tool_context
       )
+      if inspect.isawaitable(function_response):
+        function_response = await function_response
 
     if not function_response:
       function_response = await _process_function_live_helper(
@@ -235,15 +246,26 @@ async def handle_function_calls_live(
       )
 
     # Calls after_tool_callback if it exists.
+    # if agent.after_tool_callback:
+    #   new_response = agent.after_tool_callback(
+    #       tool,
+    #       function_args,
+    #       tool_context,
+    #       function_response,
+    #   )
+    #   if new_response:
+    #     function_response = new_response
     if agent.after_tool_callback:
-      new_response = agent.after_tool_callback(
-          tool,
-          function_args,
-          tool_context,
-          function_response,
+      altered_function_response = agent.after_tool_callback(
+          tool=tool,
+          args=function_args,
+          tool_context=tool_context,
+          tool_response=function_response,
       )
-      if new_response:
-        function_response = new_response
+      if inspect.isawaitable(altered_function_response):
+        altered_function_response = await altered_function_response
+      if altered_function_response is not None:
+        function_response = altered_function_response
 
     if tool.is_long_running:
       # Allow async function to return None to not provide function response.
diff --git a/tests/unittests/flows/llm_flows/test_async_tool_callbacks.py b/tests/unittests/flows/llm_flows/test_async_tool_callbacks.py
new file mode 100644
index 0000000..120755b
--- /dev/null
+++ b/tests/unittests/flows/llm_flows/test_async_tool_callbacks.py
@@ -0,0 +1,109 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import Any, Dict, Optional
+
+import pytest
+
+from google.adk.agents import Agent
+from google.adk.tools.function_tool import FunctionTool
+from google.adk.tools.tool_context import ToolContext
+from google.adk.flows.llm_flows.functions import handle_function_calls_async
+from google.adk.events.event import Event
+from google.genai import types
+
+from ... import utils
+
+
+class AsyncBeforeToolCallback:
+
+  def __init__(self, mock_response: Dict[str, Any]):
+    self.mock_response = mock_response
+
+  async def __call__(
+      self,
+      tool: FunctionTool,
+      args: Dict[str, Any],
+      tool_context: ToolContext,
+  ) -> Optional[Dict[str, Any]]:
+    return self.mock_response
+
+
+class AsyncAfterToolCallback:
+
+  def __init__(self, mock_response: Dict[str, Any]):
+    self.mock_response = mock_response
+
+  async def __call__(
+      self,
+      tool: FunctionTool,
+      args: Dict[str, Any],
+      tool_context: ToolContext,
+      tool_response: Dict[str, Any],
+  ) -> Optional[Dict[str, Any]]:
+    return self.mock_response
+
+
+async def invoke_tool_with_callbacks(
+    before_cb=None, after_cb=None
+) -> Optional[Event]:
+  def simple_fn(**kwargs) -> Dict[str, Any]:
+    return {"initial": "response"}
+
+  tool = FunctionTool(simple_fn)
+  model = utils.MockModel.create(responses=[])
+  agent = Agent(
+      name="agent",
+      model=model,
+      tools=[tool],
+      before_tool_callback=before_cb,
+      after_tool_callback=after_cb,
+  )
+  invocation_context = utils.create_invocation_context(
+      agent=agent, user_content=""
+  )
+  # Build function call event
+  function_call = types.FunctionCall(name=tool.name, args={})
+  content = types.Content(parts=[types.Part(function_call=function_call)])
+  event = Event(
+      invocation_id=invocation_context.invocation_id,
+      author=agent.name,
+      content=content,
+  )
+  tools_dict = {tool.name: tool}
+  return await handle_function_calls_async(
+      invocation_context,
+      event,
+      tools_dict,
+  )
+
+
+@pytest.mark.asyncio
+async def test_async_before_tool_callback():
+  mock_resp = {"test": "before_tool_callback"}
+  before_cb = AsyncBeforeToolCallback(mock_resp)
+  result_event = await invoke_tool_with_callbacks(before_cb=before_cb)
+  assert result_event is not None
+  part = result_event.content.parts[0]
+  assert part.function_response.response == mock_resp
+
+
+@pytest.mark.asyncio
+async def test_async_after_tool_callback():
+  mock_resp = {"test": "after_tool_callback"}
+  after_cb = AsyncAfterToolCallback(mock_resp)
+  result_event = await invoke_tool_with_callbacks(after_cb=after_cb)
+  assert result_event is not None
+  part = result_event.content.parts[0]
+  assert part.function_response.response == mock_resp