| Casei River | |
| Subdivision Type1: | Commonwealth |
| Subdivision Name1: | Puerto Rico |
| Subdivision Type2: | Municipality |
| Subdivision Name2: | Las Marías |
| Source1 Elevation: | 305 ft. |
The Casei River (Spanish; Castilian: Río Casei) is a river of Las Marías and Mayagüez, Puerto Rico.