The Diocese of Masan (Latin: Dioecesis Masanensis) is a Latin Church ecclesiastical territory or diocese of the Catholic Church in South Korea.

It is a suffragan diocese in the ecclesiastical province of the Archdiocese of Daegu.

The current bishop is Constantine Bae Ki Hyen, appointed in 2016.

On February 15, 1966 Pope Paul VI established the Diocese of Masan with territory taken from the Diocese of Busan.

This article on a Roman Catholic diocese in Asia is a stub.