diff --git a/mnist/README.md b/mnist/README.md
index 7f9b831b88..dc97bd5c53 100644
--- a/mnist/README.md
+++ b/mnist/README.md
@@ -3,4 +3,5 @@
 ```bash
 pip install -r requirements.txt
 python main.py
+# CUDA_VISIBLE_DEVICES=2 python main.py  # to specify GPU id to ex. 2
 ```