diff --git a/guides/source/api_documentation_guidelines.md b/guides/source/api_documentation_guidelines.md
index 46c90130873b7fb988063278ff9f3071809fc34d..8e9833c381526b5fa9a2cc124a6ad84dcbcb07e0 100644
--- a/guides/source/api_documentation_guidelines.md
+++ b/guides/source/api_documentation_guidelines.md
@@ -84,6 +84,11 @@ English
 
 Please use American English (*color*, *center*, *modularize*, etc). See [a list of American and British English spelling differences here](http://en.wikipedia.org/wiki/American_and_British_English_spelling_differences).
 
+Comma
+-------
+
+Please use Oxford comma (*red, white, and blue* style). See [the detail of Oxford comma](http://en.wikipedia.org/wiki/Serial_comma).
+
 Example Code
 ------------