| Saint-Didier | |
| Native Name: | (Gallo) |
| Commune Status: | Commune |
| Image Coat Of Arms: | Héraldique - fretté.svg |
| Coordinates: | 48.0956°N -1.3706°W |
| Insee: | 35264 |
| Postal Code: | 35220 |
| Arrondissement: | Fougères-Vitré |
| Canton: | Châteaugiron |
| Mayor: | Joseph Jouault[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CA Vitré Communauté |
| Elevation Min M: | 40 |
| Elevation Max M: | 97 |
| Area Km2: | 14.14 |
Saint-Didier (in French pronounced as /sɛ̃ didje/; ; Gallo: Saent-Didier) is a commune in the Ille-et-Vilaine department in Brittany in northwestern France.
Inhabitants of Saint-Didier are called déodatiens in French.