Moelwyn Mawr is a mountain in Snowdonia, North Wales and forms part of the Moelwynion.

The glaciated landscape of the mountain provides fine examples of two specific Pleistocene features.

On the north-east flank of the mountain is a terrain of patterned ground, consisting of small-scale vegetated stripes.

On the north side, a debris tongue formed by a rock glacier extends into Cwm Croesor.

Within Cwm Orthin, Conglog and Wrysgan quarries are located on the north slope of the mountain.