| São João River | |
| Pushpin Map: | Brazil |
| Source1 Location: | Rio de Janeiro state |
| Mouth Location: | Rio das Ostras, Rio de Janeiro |
| Mouth Coordinates: | -22.5963°N -41.9917°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
The São João River is a river of Rio de Janeiro state in southeastern Brazil. It runs into the Atlantic at Rio das Ostras.
Its basin includes part of the União Biological Reserve, home to a population of endangered golden lion tamarin.