The Black Mountain is a mountain range in Mid and West Wales, straddling the county boundary between Carmarthenshire and Powys and forming the westernmost range of the Brecon Beacons National Park. Its highest point is Fan Brycheiniog at 802 metres or 2,631 ft. The Black Mountain also forms a part of the recently-created Fforest Fawr Geopark.
The Black Mountain should not be confused with the Black Mountains in the east of the National Park, nor with a 703 metre (2,306 ft) summit in the Black Mountains that is confusingly also called Black Mountain. In his description of a Blak Montayne, the antiquarian John Leland refers to a massif extending between Carmarthen and Monmouth i.e. what is now considered to be the Brecon Beacons in the wider modern sense of that term, thus also including the Black Mountains and the intervening high ground of Fforest Fawr.