diff --git a/Lib/asyncio/timeouts.py b/Lib/asyncio/timeouts.py
index 09342dc7c1310b..dff70354e42cd8 100644
--- a/Lib/asyncio/timeouts.py
+++ b/Lib/asyncio/timeouts.py
@@ -114,7 +114,7 @@ async def __aexit__(
                     raise TimeoutError from exc_val
                 elif exc_val is not None:
                     self._insert_timeout_error(exc_val)
-                    if isinstance(exc_val, ExceptionGroup):
+                    if isinstance(exc_val, BaseExceptionGroup):
                         for exc in exc_val.exceptions:
                             self._insert_timeout_error(exc)
         elif self._state is _State.ENTERED:
diff --git a/Misc/NEWS.d/next/Library/2025-08-15-14-12-29.gh-issue-137549.2DaXja.rst b/Misc/NEWS.d/next/Library/2025-08-15-14-12-29.gh-issue-137549.2DaXja.rst
new file mode 100644
index 00000000000000..859b99f63e7893
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-08-15-14-12-29.gh-issue-137549.2DaXja.rst
@@ -0,0 +1,2 @@
+Modify ``__aexit__`` method of ``asyncio.Timeout`` class to handle the superclass of ExceptionGroup object.
+Patch by gunyu1019.