| Sixt-sur-Aff | |
| Native Name: | (Gallo) |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason fr ville Sixt-sur-Aff (35).svg |
| Coordinates: | 47.7767°N -2.0772°W |
| Insee: | 35328 |
| Postal Code: | 35550 |
| Arrondissement: | Redon |
| Canton: | Redon |
| Mayor: | René Riaud[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Redon Agglomération |
| Elevation Min M: | 5 |
| Elevation Max M: | 92 |
| Area Km2: | 42.50 |
Sixt-sur-Aff (in French pronounced as /sikst syʁ af/, literally Sixt on Aff; Breton: Seizh; Gallo: Sitz) is a commune in the Ille-et-Vilaine department in Brittany in northwestern France.
Inhabitants of Sixt-sur-Aff are called Sixtins in French.