Cymer Abbey (Welsh: Abaty Cymer) is a ruined Cistercian abbey near the village of Llanelltyd, just north of Dolgellau, Gwynedd, in north-west Wales, United Kingdom.
It was founded in 1198 and is now in the care of Cadw. As with other monastic sites in England and Wales, the abbey did not survive the Dissolution of the 1530s, and parts of the fabric were recycled for their dressed stone.
Situated next to a farm, the remaining ruins are open to the public at any reasonable time.