| São Martinho | |
| Settlement Type: | Municipality |
| Population Demonym: | São-Martinhense |
| Subdivision Type: | Country |
| Subdivision Name: |  Brazil |
| Subdivision Type1: | Region |
| Subdivision Type2: | State |
| Subdivision Type3: | Mesoregion |
| Subdivision Type4: | Microregion |
| Subdivision Name1: | South |
| Subdivision Name2: | Rio Grande do Sul |
| Subdivision Name3: | Noroeste Rio-Grandense |
| Subdivision Name4: | Três Passos |
| Established Title: | Founded |
| Established Date: | 27 November 1963 |
| Leader Title: | Mayor |
| Leader Name: | Jean Hunhoff (PP, 2021 - 2024) |
| Area Total Km2: | 171.245 |
| Population Total: | 5336 |
| Population As Of: | 2021 |
| Population Density Km2: | auto |
| Timezone: | BRT |
| Utc Offset: | -3 |
São Martinho is a municipality in the state of Rio Grande do Sul, Brazil. As of 2020, the estimated population was 5,380.[1]