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.