| Afon Twymyn | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Wales |
| Subdivision Type3: | Region |
| Subdivision Name3: | Powys |
| Source1: | Esgair Lwyd, Plynlimon, Powys, Wales |
| Source1 Elevation: | 480m (1,580feet) |
| Mouth Location: | River Dyfi, Cemmaes Road |
The Afon Twymyn (en|River Twymyn|italic=yes) is a river in Powys, Mid Wales.
From its source close to Dylife and head of the Pennant Valley, the river flows through Llanbrynmair before joining the River Dyfi upstream of Cemmaes Road.