| Castelnau-Magnoac | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Castelnau-Magnoac (65).svg |
| Arrondissement: | Tarbes |
| Canton: | Les Coteaux |
| Insee: | 65129 |
| Postal Code: | 65230 |
| Mayor: | Bernard Verdier[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Pays de Trie et du Magnoac |
| Coordinates: | 43.2956°N 0.5081°W |
| Elevation M: | 367 |
| Elevation Min M: | 249 |
| Elevation Max M: | 385 |
| Area Km2: | 12.56 |
Castelnau-Magnoac (pronounced as /fr/; oc|Castèthnau de Manhoac) is a commune in the Hautes-Pyrénées department in south-western France.
Castelnau-Magnoac has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Castelnau-Magnoac is . The average annual rainfall is with May as the wettest month. The temperatures are highest on average in August, at around, and lowest in January, at around . The highest temperature ever recorded in Castelnau-Magnoac was on 13 August 2003; the coldest temperature ever recorded was on 25 December 2001.