The Catholic Diocese of Busan oversees the regions of Busan Metropolitan City, Ulsan Metropolitan City, and parts of Yangsan, Gimhae, and Miryang in Gyeongsangnam-do, Korea. Its patron is Our Lady of the Rosary, and it has two cathedral churches: Namcheon Cathedral and Jungang Cathedral. The diocesan offices are located behind Namcheon Cathedral.

As of the end of 2020, the diocese had 459,563 Catholics, comprising 7.9% of the local population. There are 126 parishes, and the clergy includes three bishops(one diocesan bishop, one auxiliary bishop, and one bishop emeritus) and 375 priests as of 2022. Because of its size, the diocese is organized into eight districts in Busan and Gyeongnam and two districts in Ulsan; since 2010, the Ulsan region has been overseen by a specially appointed episcopal vicar.

The foundation of the Diocese of Busan was laid in 1890 with the establishment of the Busan Parish, created for evangelization and pastoral care in the Gyeongsang-do region. After passing through the transitional periods of the Daegu Vicariate Apostolic in 1911 and the Gyeongnam Apostolic Prefecture in 1954, the Gyeongnam Apostolic Prefecture was elevated to the Busan Vicariate Apostolic in 1957. With the installment of Bishop John Choi Jae-sun as the first bishop, the diocese began to take its full form and develop.

On April 10, 2019, Bishop Joseph Son Sam-seok was appointed as the bishop of the Diocese of Busan, and his installation Mass was celebrated on June 4, 2019.