The Old Church of St Nidan, Llanidan is a medieval church in the community of Llanidan, in Anglesey, North Wales, close to the Menai Strait. The first church on the site was established in the 7th century by St Nidan, the confessor of the monastery at Penmon, Anglesey, but the oldest parts of the present structure, are now closed and partly ruined, date from the 14th century. In about 1500 the church was enlarged by the addition of a second nave on the north side, separated from the earlier nave by an arcade of six arches.