diff --git a/src/promptflow-core/CHANGELOG.md b/src/promptflow-core/CHANGELOG.md
index 94037fa2c40..3380fe6c410 100644
--- a/src/promptflow-core/CHANGELOG.md
+++ b/src/promptflow-core/CHANGELOG.md
@@ -1,5 +1,11 @@
 # promptflow-core package
 
+## Unreleased
+
+### Bugs fixed
+
+- Added missing `os` import in `static_web_blueprint.py` ([#4042](https://github.com/microsoft/promptflow/issues/4042)).
+
 ## v1.18.1 (2025.6.10)
 
 ### Bugs fixed
diff --git a/src/promptflow-core/promptflow/core/_serving/v1/blueprint/static_web_blueprint.py b/src/promptflow-core/promptflow/core/_serving/v1/blueprint/static_web_blueprint.py
index dd9cd54a5da..5d94846372a 100644
--- a/src/promptflow-core/promptflow/core/_serving/v1/blueprint/static_web_blueprint.py
+++ b/src/promptflow-core/promptflow/core/_serving/v1/blueprint/static_web_blueprint.py
@@ -1,7 +1,7 @@
 # ---------------------------------------------------------
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # ---------------------------------------------------------
-
+import os
 from pathlib import Path
 
 import flask