| Castelnau-d'Arbieu | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Castelnau-d'Arbieu (Gers).svg |
| Arrondissement: | Condom |
| Canton: | Fleurance-Lomagne |
| Insee: | 32078 |
| Postal Code: | 32500 |
| Mayor: | Olivier Tarbouriech[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Lomagne Gersoise |
| Coordinates: | 43.8836°N 0.7056°W |
| Elevation M: | 209 |
| Elevation Min M: | 79 |
| Elevation Max M: | 231 |
| Area Km2: | 16.34 |
Castelnau-d'Arbieu (in French pronounced as /kastɛlno daʁbjø/; Occitan (post 1500);: Castèthnau d'Arbiu) is a commune in the Gers department in southwestern France.