| Saint-Martin-de-Bréthencourt | |
| Commune Status: | Commune |
| Arrondissement: | Rambouillet |
| Canton: | Rambouillet |
| Insee: | 78564 |
| Postal Code: | 78660 |
| Mayor: | Jacky Drappier[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CA Rambouillet Territoires |
| Coordinates: | 48.5103°N 1.9283°W |
| Elevation M: | 140 |
| Elevation Min M: | 107 |
| Elevation Max M: | 162 |
| Area Km2: | 16.67 |
Saint-Martin-de-Bréthencourt (in French pronounced as /sɛ̃ maʁtɛ̃ də bʁetɑ̃kuʁ/) is a commune in the Yvelines department in the Île-de-France in north-central France.