| Mynydd Llangyndeyrn | |
| Aos: | Carmarthenshire |
| Displaymap: | Wales Carmarthenshire |
| Coordinates: | 51.7973°N -4.1972°W |
| Area: | 85.2ha |
| Notifydate: | 1992 |
Mynydd Llangyndeyrn is a Site of Special Scientific Interest (SSSI)[1] in Carmarthen & Dinefwr, Wales, and a hill reaching 263 metres (863 feet), which is a Marilyn.
Mynydd Llangyndeyrn and the SSSI are located west of Drefach and north of Pontyberem. The SSSI is approximately east-west and north-south, taking the approximate shape of a horns downwards shallow crescent.[1]
The SSSI citation for Mynydd Llangyndeyrn specifies that it is "notable as one of the larger upland semi-natural areas left in south-west Wales which, unlike most others, remains lightly grazed." The site features marshy grassland, wet heath, and dry heath, and hosts the marsh fritillary butterfly (Euphydryas aurinia).[2]