| Site of Special Scientific Interest | |
| Location | Wales | 
|---|---|
| Grid reference | SN8214430535 | 
| Coordinates | 51°57′39″N3°43′00″W / 51.960767°N 3.7166736°W | 
| Interest | Biological | 
| Area | 35.42 ha | 
| Notification | 1 January 1973 | 
Waun-Ddu is a part of the Mynydd Bach that is a Site of Special Scientific Interest in Carmarthen & Dinefwr, Wales.