| Oust-Marest | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason ville fr OustMarest (Somme).svg |
| Arrondissement: | Abbeville |
| Canton: | Friville-Escarbotin |
| Insee: | 80613 |
| Postal Code: | 80460 |
| Mayor: | Jean-Claude Davergne[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CC Villes Sœurs |
| Coordinates: | 50.0436°N 1.4597°W |
| Elevation M: | 15 |
| Elevation Min M: | 7 |
| Elevation Max M: | 113 |
| Area Km2: | 5.8 |
Oust-Marest is a commune in the Somme département in Hauts-de-France in northern France.
The commune is situated on the D1015 road, some 20miles southwest of Abbeville, on the banks of the river Bresle, the border with Seine-Maritime.
The name of Oust-Marest comes from Roman origins. Possibly from a settlement named in honour of Augusta. Archaeologists have found traces of a Gallo-Roman amphitheatre and a temple in the locality.