| Marsac-sur-Don | |
| Native Name: | (Gallo) |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Marsac-sur-Don (Loire-Atlantique).svg |
| Arrondissement: | Châteaubriant-Ancenis |
| Canton: | Guémené-Penfao |
| Insee: | 44091 |
| Postal Code: | 44170 |
| Mayor: | Hervé de Trogoff[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Châteaubriant-Derval |
| Coordinates: | 47.5964°N -1.6792°W |
| Elevation Min M: | 11 |
| Elevation Max M: | 95 |
| Area Km2: | 27.68 |
Marsac-sur-Don (in French pronounced as /maʁsak syʁ dɔ̃/, literally Marsac on Don; Gallo: Marsac, Breton: Marzheg) is a commune in the Loire-Atlantique department in western France.