diff --git a/src/google/adk/flows/llm_flows/contents.py b/src/google/adk/flows/llm_flows/contents.py
index 899f819a..da4cee94 100644
--- a/src/google/adk/flows/llm_flows/contents.py
+++ b/src/google/adk/flows/llm_flows/contents.py
@@ -594,7 +594,12 @@ def _is_event_belongs_to_branch(
   """
   if not invocation_branch or not event.branch:
     return True
-  return invocation_branch.startswith(event.branch)
+  # We use dot to delimit branch nodes. To avoid simple prefix match
+  # (e.g. agent_0 unexpectedly matching agent_00), require either perfect branch
+  # match, or match prefix with an additional explicit '.'
+  return invocation_branch == event.branch or invocation_branch.startswith(
+      f'{event.branch}.'
+  )
 
 
 def _is_function_call_event(event: Event, function_name: str) -> bool:
diff --git a/tests/unittests/flows/llm_flows/test_contents_branch.py b/tests/unittests/flows/llm_flows/test_contents_branch.py
index 736909fb..23473541 100644
--- a/tests/unittests/flows/llm_flows/test_contents_branch.py
+++ b/tests/unittests/flows/llm_flows/test_contents_branch.py
@@ -58,6 +58,18 @@ async def test_branch_filtering_child_sees_parent():
           content=types.ModelContent("Child agent response"),
           branch="parent_agent.child_agent",  # Current branch - should be included
       ),
+      Event(
+          invocation_id="inv4",
+          author="child_agent",
+          content=types.ModelContent("Excluded response 1"),
+          branch="parent_agent.child_agent000",  # Prefix match BUT not itself/ancestor - should be excluded
+      ),
+      Event(
+          invocation_id="inv5",
+          author="child_agent",
+          content=types.ModelContent("Excluded response 2"),
+          branch="parent_agent.child",  # Prefix match BUT not itself/ancestor - should be excluded
+      ),
   ]
   invocation_context.session.events = events