| Allen River | |
| Pushpin Map: | New Zealand#New Zealand South Island |
| Pushpin Map Size: | 270px |
| Pushpin Map Caption: | Mouth of the Allen River |
| Source1: | Allen Range |
| Source1 Coordinates: | -41.3999°N 172.2723°W |
| Source2: | Allen Range |
| Source2 Coordinates: | -41.416°N 172.3413°W |
| Mouth Location: | Mōkihinui River North Branch |
| Mouth Elevation: | 310m (1,020feet) |
| Mouth Coordinates: | -41.4775°N 172.2892°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | New Zealand |
| Progression: | Allen River → Mōkihinui River North Branch → Mōkihinui River → Karamea Bight → Tasman Sea |
| Tributaries Right: | Johnson River |
The Allen River is a river in the West Coast district of the South Island of New Zealand. It drains the south side of the Allen Range, elevations to 1450m (4,760feet), which forms part of the boundary between West Coast and Tasman districts. The river has left and right branches for half its length, and the right branch has a major tributary stream in a valley between the two branches. The united river flows south through a narrow gorge and is joined by the Johnson River 200m (700feet) upstream of its confluence with the North branch of the Mōkihinui River.