| Petit-Mars | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Petit-Mars (Loire-Atlantique).svg |
| Arrondissement: | Châteaubriant-Ancenis |
| Canton: | Nort-sur-Erdre |
| Insee: | 44122 |
| Postal Code: | 44390 |
| Mayor: | Jean-Luc Besnier[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Erdre et Gesvres |
| Coordinates: | 47.395°N -1.4539°W |
| Elevation Min M: | 2 |
| Elevation Max M: | 43 |
| Area Km2: | 25.97 |
Petit-Mars is a commune in the Loire-Atlantique department in western France.