| Lamastre | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Lamastre (Ardèche).svg |
| Arrondissement: | Tournon-sur-Rhône |
| Canton: | Haut-Vivarais |
| Insee: | 07129 |
| Postal Code: | 07270 |
| Mayor: | Jean-Paul Vallon[1] |
| Term: | 2020 - 2026 |
| Coordinates: | 44.9864°N 4.5817°W |
| Elevation Min M: | 342 |
| Elevation Max M: | 860 |
| Area Km2: | 25.45 |
Lamastre (in French pronounced as /lamastʁ/; Occitan (post 1500);: La Mastra) is a commune in the Ardèche department in southern France. It lies on the river Doux. The Chemin de fer du Vivarais, a metre-gauge tourist railway, connects Lamastre with Tournon-sur-Rhône.