| Site of Special Scientific Interest | |
  Location within Carmarthenshire | |
| Location | Carmarthen & Dinefwr |
|---|---|
| Grid reference | SN 579 216 |
| Coordinates | 51°52′31″N 4°03′54″W / 51.8753°N 4.06489°W |
| Interest | Biological |
| Area | 6 hectares (15 acres) |
| Notification | 1973 |
Allt y Wern is a Site of Special Scientific Interest (SSSI) in the community of Llangathen in Carmarthenshire, Wales. The site is a semi-natural broadleaved woodland with an area of 6 hectares (15 acres).