diff --git a/package/samplers/auto_sampler/README.md b/package/samplers/auto_sampler/README.md
index efeefd6f..78ffb581 100644
--- a/package/samplers/auto_sampler/README.md
+++ b/package/samplers/auto_sampler/README.md
@@ -27,6 +27,8 @@ This sampler requires optional dependencies of Optuna.
 $ pip install optunahub cmaes torch scipy
 ```
 
+Note that since we may update the implementation of `AutoSampler`, it is highly encouraged to use the latest version of Optuna.
+
 ## Example
 
 ```python
diff --git a/package/samplers/auto_sampler/requirements.txt b/package/samplers/auto_sampler/requirements.txt
index 52b403bd..10fd7a0f 100644
--- a/package/samplers/auto_sampler/requirements.txt
+++ b/package/samplers/auto_sampler/requirements.txt
@@ -1,4 +1,3 @@
 scipy
 torch
 cmaes
-optuna>=4.1.0