| Jurisdiction: | Diocese |
| Tunduru–Masasi | |
| Latin: | Dioecesis Tunduruensis–Masasiensis |
| Country: | Tanzania |
| Metropolitan: | Songea |
| Rite: | Latin Rite |
| Area Km2: | 22,730 |
| Population: | 669,854 |
| Population As Of: | 2004 |
| Catholics: | 90,740 |
| Catholics Percent: | 13.5 |
| Bishop: | Filbert Felician Mhasi |
The Roman Catholic Diocese of Tunduru–Masasi (Latin: Dioecesis Tunduruensis–Masasiensis) is a diocese located in Tunduru–Masasi in the ecclesiastical province of Songea in Tanzania.
The diocese has an area covering 22,730 square kilometers. In the East region borders with the diocese of Mtwara, the Northeast diocese of Lindi, Mozambique to the South, to the West the Archdiocese of Songea. There are now 24 local priests and 19 parishes. The diocese is in the extreme Southern part of Tanzania close to the border with Mozambique. It is surrounded by the Selous Game Reserve.