diff --git a/physbo/__init__.py b/physbo/__init__.py
index b1435725..b3512ca9 100644
--- a/physbo/__init__.py
+++ b/physbo/__init__.py
@@ -14,4 +14,4 @@
 from .predictor import base_predictor
 from .variable import variable
 
-__version__ = "2.0.1"
+__version__ = "2.1-dev"
diff --git a/setup.cfg b/setup.cfg
index 7339eaf6..0a58bc54 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,6 +1,6 @@
 [metadata]
 name = physbo
-version = 2.0.1
+version = 2.1.dev1
 description = optimization tool for PHYSics based on Bayesian Optimization
 long_description = file: README.md
 long_description_content_type = text/markdown