| Clain | |
| Map: | Clain (rivière).png |
| Mouth Location: | Vienne |
| Mouth Coordinates: | 46.7811°N 0.5406°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | France |
| Length: | 144km (89miles) |
| Basin Size: | 3145km2 |
The Clain (pronounced as /fr/; oc|Clen|link=yes) is a 144km (89miles) long river in western France, a left tributary of the river Vienne. Its source is near Hiesse, Charente.
The Clain flows generally north, through the following departments and towns:
It joins the Vienne near Châtellerault, Cenon-sur-Vienne.
Among its tributaries are the Boivre, the Clouère and the Vonne.