diff --git a/samples/agent/adk/contact_lookup/prompt_builder.py b/samples/agent/adk/contact_lookup/prompt_builder.py
index 3fe269e6..ffd1ee33 100644
--- a/samples/agent/adk/contact_lookup/prompt_builder.py
+++ b/samples/agent/adk/contact_lookup/prompt_builder.py
@@ -113,6 +113,6 @@ def get_text_prompt() -> str:
     my_base_url = "http://localhost:8000"
     contact_prompt = get_ui_prompt(my_base_url, CONTACT_UI_EXAMPLES)
     print(contact_prompt)
-    with open("generated_prompt.txt", "w") as f:
+    with open("generated_prompt.txt", "w", encoding="utf-8") as f:
         f.write(contact_prompt)
     print("\nGenerated prompt saved to generated_prompt.txt")
diff --git a/samples/agent/adk/contact_lookup/tools.py b/samples/agent/adk/contact_lookup/tools.py
index 56c9e15e..4a73c4b7 100644
--- a/samples/agent/adk/contact_lookup/tools.py
+++ b/samples/agent/adk/contact_lookup/tools.py
@@ -34,7 +34,7 @@ def get_contact_info(name: str, tool_context: ToolContext, department: str = "")
     try:
         script_dir = os.path.dirname(__file__)
         file_path = os.path.join(script_dir, "contact_data.json")
-        with open(file_path) as f:
+        with open(file_path, encoding='utf-8') as f:
             contact_data_str = f.read()
             if base_url := tool_context.state.get("base_url"):                
                 contact_data_str = contact_data_str.replace("http://localhost:10002", base_url)
diff --git a/samples/agent/adk/restaurant_finder/prompt_builder.py b/samples/agent/adk/restaurant_finder/prompt_builder.py
index 1cc8445e..98499266 100644
--- a/samples/agent/adk/restaurant_finder/prompt_builder.py
+++ b/samples/agent/adk/restaurant_finder/prompt_builder.py
@@ -859,6 +859,6 @@ def get_text_prompt() -> str:
     print(restaurant_prompt)
 
     # This demonstrates how you could save the prompt to a file for inspection
-    with open("generated_prompt.txt", "w") as f:
+    with open("generated_prompt.txt", "w", encoding="utf-8") as f:
         f.write(restaurant_prompt)
     print("\nGenerated prompt saved to generated_prompt.txt")
diff --git a/samples/agent/adk/restaurant_finder/tools.py b/samples/agent/adk/restaurant_finder/tools.py
index 6a6dd453..a8c73b3a 100644
--- a/samples/agent/adk/restaurant_finder/tools.py
+++ b/samples/agent/adk/restaurant_finder/tools.py
@@ -34,7 +34,7 @@ def get_restaurants(cuisine: str, location: str,  tool_context: ToolContext, cou
         try:
             script_dir = os.path.dirname(__file__)
             file_path = os.path.join(script_dir, "restaurant_data.json")
-            with open(file_path) as f:
+            with open(file_path, encoding='utf-8') as f:
                 restaurant_data_str = f.read()
                 if base_url := tool_context.state.get("base_url"):                    
                     restaurant_data_str = restaurant_data_str.replace("http://localhost:10002", base_url)