| Castelnau de Brassac | |
| Image Coat Of Arms: | Blason ville fr Castelnau-de-Brassac (Tarn).svg |
| Arrondissement: | Castres |
| Canton: | Les Hautes Terres d'Oc |
| Insee: | 81062 |
| Postal Code: | 81260 |
| Commune: | Fontrieu |
| Coordinates: | 43.6497°N 2.515°W |
| Elevation M: | 520 |
| Elevation Min M: | 396 |
| Elevation Max M: | 1137 |
| Area Km2: | 72.88 |
| Population: | 733 |
| Population Date: | 2018 |
| Population Footnotes: | [1] |
Castelnau-de-Brassac (in French pronounced as /kastɛlno də bʁasak/; Languedocien: Castèlnòu de Braçac) is a former commune in the Tarn department in southern France. On 1 January 2016, it was merged into the new commune of Fontrieu.[2]