Mynydd Llysiau is a subsidiary summit of Waun Fach in the Black Mountains in south-eastern Wales.

It lies halfway between Waun Fach and Pen Allt-mawr.

It is a distinguished summit with a steep eastern face.

The summit, marked by a pile of stones, is long grassy ridge.

To the south is Pen Twyn Glas, before which are two boundary stones that resemble grave stones.