Mynydd Mawr (Welsh for 'big mountain') is a mountain in Snowdonia, North Wales, approximately 7 km (4.3 mi) west of Snowdon itself, overlooking Llyn Cwellyn and being the northern outlier of the Moel Hebog group.

A popular ascent starts from Rhyd Ddu.

On its western flank are the remains of ancient settlements and field systems.

[1] The summit offers extensive views, on a clear day to the west, the views extend to the Llŷn Peninsula and Caernarfon Bay, from the north-west includes Anglesey.

On exceptionally clear days, the Wicklow Mountains in Ireland can be seen westwards across the Irish Sea from the summit.