| Saint-Martin-sur-Oust | |
| Native Name: | Sant-Varzhin-an-Oud |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Saint-Martin-sur-Oust (Morbihan).svg |
| Coordinates: | 47.7466°N -2.2525°W |
| Insee: | 56229 |
| Postal Code: | 56200 |
| Arrondissement: | Vannes |
| Canton: | Guer |
| Mayor: | Marion Le Pogam[1] |
| Term: | 2020 - 2026 |
| Elevation Min M: | 2 |
| Elevation Max M: | 103 |
| Area Km2: | 28.24 |
Saint-Martin-sur-Oust (in French pronounced as /sɛ̃ maʁtɛ̃ syʁ ust/, literally Saint-Martin on Oust; Breton: Sant-Varzhin-an-Oud) is a commune in the Morbihan department of Brittany in north-western France. Until 6 October 2008 it was known as Saint-Martin.[2] Inhabitants of Saint-Martin-sur-Oust are called in French Martinais.