Llanthony Priory () is a partly ruined former Augustinian priory in the secluded Vale of Ewyas, a steep-sided once-glaciated valley within the Black Mountains area of the Brecon Beacons National Park in Monmouthshire, south east Wales. It lies seven miles north of Abergavenny on an old road to Hay-on-Wye at Llanthony. The priory ruins lie to the west of the prominent Hatterrall Ridge, a limb of the Black mountains. The main ruins are under the care of Cadw and entrance is free.