| Lassy | |
| Native Name: | (Gallo) |
| Commune Status: | Commune |
| Coordinates: | 47.9797°N -1.8686°W |
| Insee: | 35149 |
| Postal Code: | 35580 |
| Arrondissement: | Redon |
| Canton: | Guichen |
| Mayor: | Didier Le Chénéchal[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Vallons de Haute-Bretagne |
| Elevation Min M: | 37 |
| Elevation Max M: | 112 |
| Area Km2: | 9.76 |
Lassy (in French pronounced as /lasi/; Breton: Lazig; Gallo: Laczic) is a commune in the Ille-et-Vilaine department of Brittany in northwestern France.
Inhabitants of Lassy are called in French Lasséens.