| São Nicolau | |
| Settlement Type: | Municipality |
| Pushpin Map: | Brazil |
| Pushpin Map Caption: | Location in Brazil |
| Coordinates: | -28.1828°N -55.2669°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Brazil |
| Subdivision Type1: | State |
| Subdivision Name1: | Rio Grande do Sul |
| Subdivision Type2: | Meso-region |
| Subdivision Name2: | Noroeste Rio-Grandense --> |
| Subdivision Type3: | Micro-region |
| Subdivision Name3: | Santo Ângelo |
| Leader Title: | Prefect |
| Area Total Km2: | 485.32 |
| Population Total: | 5,208 |
| Population As Of: | 2020[1] |
| Population Density Km2: | auto |
| Timezone1: | BRT |
| Utc Offset1: | -3 |
| Postal Code Type: | Postal code |
| Area Code Type: | Phone code |
São Nicolau (Portuguese meaning Saint Nicholas) is a municipality of the state of Rio Grande do Sul, Brazil. It was founded in 1626 by Jesuit priest Roque González y de Santa Cruz.[2] The population is 5,208 (2020 est.) in an area of 485.32 km².[3] It is located 562 km west of the state capital of Porto Alegre, northeast of Alegrete. The Uruguay River, which forms the border with Argentina, flows along the northwestern part of the municipality.
The municipality would be partially flooded by the proposed Garabí Dam.