| Os-Marsillon | |
| Commune Status: | Commune |
| Arrondissement: | Pau |
| Canton: | Le Cœur de Béarn |
| Insee: | 64431 |
| Postal Code: | 64150 |
| Mayor: | Jérôme Toulouse[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Lacq-Orthez |
| Coordinates: | 43.3897°N -0.6144°W |
| Elevation M: | 101 |
| Elevation Min M: | 92 |
| Elevation Max M: | 151 |
| Area Km2: | 5.45 |
Os-Marsillon (in French pronounced as /ɔs maʁsijɔ̃/; Occitan (post 1500);: Òs e Marcelhon) is a commune in the Pyrénées-Atlantiques department in south-western France.