Mynydd Llangyndeyrn

Mynydd Llangyndeyrn is a Site of Special Scientific Interest (SSSI) 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 1.3 mi east-west and 0.3 mi north-south, taking the approximate shape of a horns downwards shallow crescent.

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).