| Castelvieilh | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr Castelvieilh (65).svg |
| Arrondissement: | Tarbes |
| Canton: | Les Coteaux |
| Insee: | 65131 |
| Postal Code: | 65350 |
| Mayor: | Jean-Marc Castor[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Coteaux du Val d'Arros |
| Coordinates: | 43.2847°N 0.1967°W |
| Elevation M: | 366 |
| Elevation Min M: | 223 |
| Elevation Max M: | 360 |
| Area Km2: | 5.31 |
Castelvieilh (pronounced as /fr/; oc|Castèthvièlh) is a commune in the Hautes-Pyrénées department in south-western France.
Castelvieilh has an oceanic climate (Köppen climate classification Cfb) closely bordering on a humid subtropical climate (Cfa). The average annual temperature in Castelvieilh 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 Castelvieilh was on 4 August 2003; the coldest temperature ever recorded was on 8 February 2012.