The Roman Catholic Diocese of Mafinga (; ) is a diocese located in Mafinga in the ecclesiastical province of Mbeya in Tanzania.
The Diocese of Mafinga was erected by Pope Francis from the Diocese of Iringa on December 22, 2023, and Vincent Cosmas Mwagala was named the first ordinary. The diocese was canonically inaugurated by Angelo Accattino in the evening before Saint Joseph's Day. The following day, March 19, 2024, Mwagala received episcopal consecration and became the diocese's first bishop.