| Castelnau-sur-l'Auvignon | |
| Commune Status: | Commune |
| Arrondissement: | Condom |
| Canton: | Baïse-Armagnac |
| Insee: | 32080 |
| Postal Code: | 32100 |
| Mayor: | Maurice Boison[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Ténarèze |
| Coordinates: | 43.9728°N 0.4578°W |
| Elevation M: | 166 |
| Elevation Min M: | 98 |
| Elevation Max M: | 209 |
| Area Km2: | 10.22 |
Castelnau-sur-l'Auvignon (in French pronounced as /kastɛlno syʁ loviɲɔ̃/; Occitan (post 1500);: Castèthnau d'Auvinhon) is a commune in the Gers department in southwestern France.