diff --git a/scripts/check_new_py_files.py b/scripts/check_new_py_files.py
index e8f9844512c..deb63413c47 100644
--- a/scripts/check_new_py_files.py
+++ b/scripts/check_new_py_files.py
@@ -213,7 +213,7 @@ def get_vcs_added_files(root: str = '.') -> set[str] | None:
             p = parts[1].strip()
             if jj_root and not os.path.isabs(p):
               p = os.path.join(jj_root, p)
-            added.add(p)
+            added.add(p.replace(os.sep, '/'))
       return added
 
   # 3. hg
@@ -222,9 +222,11 @@ def get_vcs_added_files(root: str = '.') -> set[str] | None:
     if code == 0:
       _, out = _run_cmd(['hg', 'status', '--added', '--no-status'], cwd=root)
       return {
-          os.path.join(hg_root, f.strip())
-          if (hg_root and not os.path.isabs(f.strip()))
-          else f.strip()
+          (
+              os.path.join(hg_root, f.strip())
+              if (hg_root and not os.path.isabs(f.strip()))
+              else f.strip()
+          ).replace(os.sep, '/')
           for f in out.splitlines()
           if f.strip()
       }
diff --git a/tests/unittests/scripts/test_check_new_py_files.py b/tests/unittests/scripts/test_check_new_py_files.py
index cf90d8ff2b5..9f46ce94487 100644
--- a/tests/unittests/scripts/test_check_new_py_files.py
+++ b/tests/unittests/scripts/test_check_new_py_files.py
@@ -16,6 +16,7 @@
 
 from __future__ import annotations
 
+import ntpath
 import os
 import pathlib
 import subprocess
@@ -463,7 +464,15 @@ def fake_run_cmd(cmd: list[str], cwd: str | None = None) -> tuple[int, str]:
   assert added == {'src/google/adk/agents/_committed.py'}
 
 
-def test_get_vcs_added_files_jj(monkeypatch: pytest.MonkeyPatch) -> None:
+def _patch_windows_paths(monkeypatch: pytest.MonkeyPatch) -> None:
+  monkeypatch.setattr(check_new_py_files.os, 'path', ntpath)
+  monkeypatch.setattr(check_new_py_files.os, 'sep', '\\')
+
+
+@pytest.mark.parametrize('windows', [False, True])
+def test_get_vcs_added_files_jj(
+    monkeypatch: pytest.MonkeyPatch, windows: bool
+) -> None:
   def fake_which(cmd: str) -> str | None:
     return '/usr/bin/' + cmd if cmd == 'jj' else None
 
@@ -476,12 +485,17 @@ def fake_run_cmd(cmd: list[str], cwd: str | None = None) -> tuple[int, str]:
 
   monkeypatch.setattr(check_new_py_files.shutil, 'which', fake_which)
   monkeypatch.setattr(check_new_py_files, '_run_cmd', fake_run_cmd)
+  if windows:
+    _patch_windows_paths(monkeypatch)
 
   added = check_new_py_files.get_vcs_added_files('.')
   assert added == {'/workspace/src/google/adk/agents/_jj_agent.py'}
 
 
-def test_get_vcs_added_files_hg(monkeypatch: pytest.MonkeyPatch) -> None:
+@pytest.mark.parametrize('windows', [False, True])
+def test_get_vcs_added_files_hg(
+    monkeypatch: pytest.MonkeyPatch, windows: bool
+) -> None:
   def fake_which(cmd: str) -> str | None:
     return '/usr/bin/' + cmd if cmd == 'hg' else None
 
@@ -494,6 +508,8 @@ def fake_run_cmd(cmd: list[str], cwd: str | None = None) -> tuple[int, str]:
 
   monkeypatch.setattr(check_new_py_files.shutil, 'which', fake_which)
   monkeypatch.setattr(check_new_py_files, '_run_cmd', fake_run_cmd)
+  if windows:
+    _patch_windows_paths(monkeypatch)
 
   added = check_new_py_files.get_vcs_added_files('.')
   assert added == {'/workspace/src/google/adk/agents/_hg_agent.py'}