| Castelnau-Montratier | |
| Image Coat Of Arms: | Blason de la ville de Castelnau-Montratier (Lot).svg |
| Arrondissement: | Cahors |
| Canton: | Marches du Sud-Quercy |
| Commune: | Castelnau-Montratier |
| Insee: | 46063 |
| Postal Code: | 46170 |
| Coordinates: | 44.2697°N 1.3539°W |
| Elevation M: | 248 |
| Elevation Min M: | 108 |
| Elevation Max M: | 295 |
| Area Km2: | 72.54 |
| Population: | 1727 |
| Population Date: | 2019 |
| Population Footnotes: | [1] |
Castelnau-Montratier (in French pronounced as /kastɛlno mɔ̃ʁatje/; Languedocien: Castèlnau de Montratièr) is a former commune in the Lot department in south-western France. On 1 January 2017, it was merged into the new commune Castelnau-Montratier-Sainte-Alauzie,[2] which was renamed Castelnau-Montratier effective 2024.
The Barguelonne flows southwestward through the northern part of the commune.