| Jurisdiction: | Diocese |
| San Martín | |
| Latin: | Dioecesis Foromartiniensis |
| Local: | Diócesis de San Martín |
| Country: | Argentina |
| Metropolitan: | Buenos Aires |
| Province: | Buenos Aires |
| Area Km2: | 102 |
| Population: | 769,000 |
| Population As Of: | 2010 |
| Catholics: | 538,000 |
| Catholics Percent: | 70 |
| Parishes: | 37 |
| Denomination: | Roman Catholic |
| Rite: | Roman Rite |
| Established: | 10 April 1961 (years ago) |
| Cathedral: | Cathedral of Christ the Good Shepherd in San Martín |
| Patron: | St Joseph the Worker Our Lady of Lourdes |
| Bishop Title: | Bishop |
| Bishop: | Martín Fassi |
| Metro Archbishop: | Mario Aurelio Poli |
| Auxiliary Bishops: | Ham Lim Moon |
The Roman Catholic Diocese of San Martín is located in the city of San Martín, Buenos Aires, Argentina. It was established by Saint John XXIII on 10 April 1961.