| San Lorenzo a Merse | |
| Coordinates: | 43.1472°N 11.2717°W |
| Province: | Siena (SI) |
| Comune: | Monticiano |
| Elevation M: | 227 |
| Population Total: | 164 |
| Population As Of: | 2011 |
| Gentilic: | Sanlorenzini |
San Lorenzo a Merse is a village in Tuscany, central Italy, administratively a frazione of the comune of Monticiano, province of Siena. At the time of the 2001 census its population was 164.[1]