diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index b5228ca4..270a4cc9 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -17,6 +17,7 @@ jobs:
           python-version: '3.x'
           architecture: x64
       - name: Install dependencies
+        # python_tests requires optuna>=3.0.0 since it imports FloatDistribution
         run: |
           python -m pip install --progress-bar off --upgrade pip setuptools
           pip install --progress-bar off "optuna>=3.0.0"
@@ -30,7 +31,9 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        # Add Python '3.11' after released Optuna v3.1
+        # since Optuna v3.0.4 depends on scipy<1.9.0 and >=1.7.0
+        python-version: ['3.7', '3.8', '3.9', '3.10']
     steps:
       - uses: actions/checkout@v2
       - name: Setup Python${{ matrix.python-version }}
@@ -39,6 +42,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
           architecture: x64
       - name: Install dependencies
+        # python_tests requires optuna>=3.0.0 since it imports FloatDistribution
         run: |
           python -m pip install --progress-bar off --upgrade pip setuptools
           pip install --progress-bar off "optuna>=3.0.0"