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.

[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.

This geographical article relating to Rio Grande do Sul is a stub.