diff --git a/setup.py b/setup.py
index 1860995..f71cf2c 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,6 @@ def get_install_requires():
 
     return [
         "plotly",
-        "pandas",  # required for plotly express
     ]
 
 
@@ -47,6 +46,7 @@ def get_extras_require():
             # test
             "pytest",
             # document
+            "pandas",  # required for plotly express
             "sphinx==3.0.4",
             "sphinx-rtd-theme",
         ]