| Leff | |
| Pushpin Map: | France#France Bretagne |
| Mouth Coordinates: | 48.7271°N -3.1322°W |
| Subdivision Type1: | Country |
| Length: | 62.4km (38.8miles) |
The Leff (Breton: Leñv) is a river in Brittany, France. It is 62.4km (38.8miles) long. It flows into the Trieux near Pontrieux.
In the valley of Leff, there is a town called Châtelaudren.[1]