Mynydd Llwydiarth is a mountain in southern Snowdonia, Wales.

[2] It is a long ridge running from a low summit to the south of Mynydd Dolgoed, running south-west to Mynydd Cymerau.

Nant Llwydiarth rises on the south flank of the mountain, and on the west slope the Ratgoed slate quarry operated until 1946.

[3] It is one of the Dyfi hills.