| Bains-sur-Oust | |
| Native Name: | (Gallo) |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Bains-sur-Oust (Ille-et-Vilaine).svg |
| Coordinates: | 47.7044°N -2.0703°W |
| Insee: | 35013 |
| Postal Code: | 35600 |
| Arrondissement: | Redon |
| Canton: | Redon |
| Mayor: | Daniel Barre[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Redon Agglomération |
| Elevation Min M: | 0 |
| Elevation Max M: | 89 |
| Area Km2: | 44.63 |
Bains-sur-Oust (in French pronounced as /bɛ̃ syʁ ust/, literally Bains on Oust;, Gallo: Bein) is a commune in the Ille-et-Vilaine departement in Brittany in northwestern France.
Inhabitants of Bains-sur-Oust are called Bainsois in French.