The Roman Catholic Diocese of Masan (Hangul/Hanja/Latin: 천주교 마산교구/天主敎馬山敎區/Dioecesis Masanensis) is a diocese of the Latin Rite of the Catholic Church located in Masan District of the Unified Changwon City, Southern Gyeongsang Province. The namesake of the diocese - Masan was a municipal city in Southern Gyeongsang which consists only two districts - known as Happo-gu and Hoewon-gu. On July 1st 2010, this city was later integrated with Changwon and Jinhae Cities to form the Unified Changwon City which consists five districts and these include districts in Masan as well (Present-day Changwon MasanHappo-gu and Changwon MasanHoewon-gu). The diocese is a suffragan to the Archdiocese of Daegu. The current bishop of this diocese is Francis Xavier Ahn Myeong-ok.
Diocese of Masan was formed in February 15th 1966 by Pope Paul VI from the claimed territories of the Diocese of Busan - majorly in Southern Gyeongsang Province. Only three cities in Southern Gyeongsang - Gimhae, Yangsan and Miryang remain in the Diocese of Busan with some exceptions on particular communes which covered by Diocese of Masan:
- Gimhae (JinYeong-eup and Jillye-myeon)
- Miryang (Cheongdo-myeon, Muan-myeon, Bubuk-myeon, Chodong-myeon and Hanam-eup)
Its mother church is Yangdeok Cathedral of the Sacred Heart (양덕성당/陽德聖堂), located at 128 Yangdeog-yet 2-gil/양덕옛2길, Yangdeok 2-dong 72-7 beonji, Changwon MasanHoewon-gu, Southern Gyeongsang Province. The cathedral is designed by Kim Swoo-geun (김수근/金壽根; Born: February 20th 1931 - Died: June 14th 1986), a prominent Korean Architect who designed Seoul Olympic Stadium in Seoul Songpa-gu for 1988 Summer Olympics.
The cathedral is not too big, but it gives off a warm, cozy feeling. Similar as Kyungdong Presbyterian Church in Seoul Jung-gu which is designed by the same architect, it uses red brick and you must climb a set of steps before entering inside the cathedral. With a skylight above the altar, the design uses sunlight to great effect.