diff --git a/src/google/adk/tools/retrieval/vertex_ai_rag_retrieval.py b/src/google/adk/tools/retrieval/vertex_ai_rag_retrieval.py
index 4d564ca164..f54322cc11 100644
--- a/src/google/adk/tools/retrieval/vertex_ai_rag_retrieval.py
+++ b/src/google/adk/tools/retrieval/vertex_ai_rag_retrieval.py
@@ -17,6 +17,7 @@
 from __future__ import annotations
 
 import logging
+import asyncio
 from typing import Any
 from typing import TYPE_CHECKING
 
@@ -94,8 +95,9 @@ async def run_async(
   ) -> Any:
     from ...dependencies.vertexai import rag
 
-    response = rag.retrieval_query(
-        text=args['query'],
+    response = await asyncio.to_thread(
+        rag.retrieval_query,
+        text=args["query"],
         rag_resources=self.vertex_rag_store.rag_resources,
         rag_corpora=self.vertex_rag_store.rag_corpora,
         similarity_top_k=self.vertex_rag_store.similarity_top_k,