| Fesmy-le-Sart | |
| Commune Status: | Commune |
| Arrondissement: | Vervins |
| Canton: | Guise |
| Insee: | 02308 |
| Postal Code: | 02450 |
| Mayor: | Gaspard Riou[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Thiérache du Centre |
| Coordinates: | 50.0425°N 3.6792°W |
| Elevation M: | 150 |
| Elevation Min M: | 137 |
| Elevation Max M: | 192 |
| Area Km2: | 16.06 |
Fesmy-le-Sart (pronounced as /fr/) is a commune in the Aisne department in Hauts-de-France in northern France.