| Isla San Martín | |
| Image Caption: | Isla San Martín |
| Map: | Mexico |
| Location: | Gulf of California |
| Coordinates: | 30.4889°N -116.1141°W |
| Elevation M: | 125 |
| Country: | Mexico |
| Country Admin Divisions Title: | State |
| Country Admin Divisions: | Baja California |
| Population: | uninhabited |
Isla San Martín is an island in the Pacific Ocean west of the Baja California Peninsula. The island is uninhabited and is part of the Ensenada Municipality.
Isla San Martín has six species of reptiles: Anniella geronimensis (Baja California legless lizard), Diadophis punctatus (ring-necked snake), Elgaria multicarinata (southern alligator lizard), Hypsiglena ochrorhynchus (coast night snake), Pituophis catenifer (gopher snake), and Uta stansburiana (common side-blotched lizard).
Formerly, the San Martin Island woodrat lived on the island, until it became extinct due to predation by feral cats.