| Nant Llwydiarth | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Wales |
| Source1: | Mynydd Hendre-ddu |
| Source1 Elevation: | 1200feet |
| Mouth Location: | Pont Cymerau, Aberllefenni |
| Mouth Coordinates: | 52.6778°N -3.8084°W |
The Nant Llwydiarth is a small river in Mid Wales. It flows from the southern flank of Mynydd Hendre-ddu down to Pont Cymerau, north-east of Aberllefenni.[1] Here it joins the Nant Ceiswyn to form the Afon Dulas that flows south to the Afon Dyfi. There was an ancient bridge at Pont Cymerau.[2]