diff --git a/optuna_dashboard/_app.py b/optuna_dashboard/_app.py
index 98571add..caf2be02 100644
--- a/optuna_dashboard/_app.py
+++ b/optuna_dashboard/_app.py
@@ -27,7 +27,6 @@ from bottle import static_file
 from optuna.exceptions import DuplicatedStudyError
 from optuna.storages import BaseStorage
 from optuna.storages import RDBStorage
-from optuna.storages import RedisStorage
 from optuna.study import StudyDirection
 from optuna.study import StudySummary
 from optuna.trial import FrozenTrial
@@ -393,7 +392,9 @@ def _frozen_study_to_study_summary(frozen_study: "FrozenStudy") -> StudySummary:
 def get_storage(storage: Union[str, BaseStorage]) -> BaseStorage:
     if isinstance(storage, str):
         if storage.startswith("redis"):
-            return RedisStorage(storage)
+            raise ValueError(
+                "RedisStorage is unsupported from Optuna v3.1 or Optuna Dashboard v0.8.0"
+            )
         else:
             return RDBStorage(storage, skip_compatibility_check=True)
     return storage
diff --git a/optuna_dashboard/_cli.py b/optuna_dashboard/_cli.py
index 59288386..1b3d3fca 100644
--- a/optuna_dashboard/_cli.py
+++ b/optuna_dashboard/_cli.py
@@ -9,7 +9,6 @@ from bottle import Bottle
 from bottle import run
 from optuna.storages import BaseStorage
 from optuna.storages import RDBStorage
-from optuna.storages import RedisStorage
 
 from . import __version__
 from ._app import create_app
@@ -99,7 +98,7 @@ def main() -> None:
 
     storage: BaseStorage
     if args.storage.startswith("redis"):
-        storage = RedisStorage(args.storage)
+        raise ValueError("RedisStorage is unsupported from Optuna v3.1 or Optuna Dashboard v0.8.0")
     else:
         storage = RDBStorage(args.storage, skip_compatibility_check=True)
 
diff --git a/visual_regression_test.py b/visual_regression_test.py
index 3e259d7f..aa1050da 100644
--- a/visual_regression_test.py
+++ b/visual_regression_test.py
@@ -212,8 +212,6 @@ def main() -> None:
     storage: optuna.storages.BaseStorage
     if not args.storage:
         storage = create_dummy_storage()
-    elif args.storage.startswith("redis"):
-        storage = optuna.storages.RedisStorage(args.storage)
     else:
         storage = optuna.storages.RDBStorage(args.storage)