diff --git a/optuna/storages/_base.py b/optuna/storages/_base.py
index b15aa4204a..1a499e3c36 100644
--- a/optuna/storages/_base.py
+++ b/optuna/storages/_base.py
@@ -71,7 +71,6 @@ def create_new_study(
             :exc:`optuna.exceptions.DuplicatedStudyError`:
                 If a study with the same ``study_name`` already exists.
         """
-        # TODO(ytsmiling) Fix RDB storage implementation to ensure unique `study_id`.
         raise NotImplementedError
 
     @abc.abstractmethod