Monastery of Mohill-Manchan, Early Christian monastery ruins in Mohill, County Leitrim, Ireland.

The monastery of Mohill-Manchan stood at Mohill, County Leitrim, on an estate of roughly 300 to 600 acres reaching across the river to the townlands of Tullybradan, Lisdadanan, Coolabaun, Cappagh, Gortfadda, Drumcroy and Drumkilla. Its buildings are not described in the sources; St. Mary's Church, Mohill, was built from the ruins in the 18th century.

Manchán of Mohill founded a church here in the 6th century, and the community's estate later covered townlands on both sides of the river. About 1216 it became an Augustinian priory dedicated to Saint Mary, in the diocese of Ardagh. It was suppressed in the late 16th century, briefly revived under Confederate Ireland with Canon Antony Mag Raghnaill appointed prior on 21 August 1648, and suppressed again by Cromwellian forces around 1649–1653.

The Irish name is mainistir an Maothail-Manachain, and the site takes its name from Manchán of Mohill, who founded a church here in the 6th century. The Annals of the Four Masters record that in 1166 Ruaidhrí Ua Conchobhair covered Manchán's shrine with gold embroidery. In 1430 the priory held the right to offer sanctuary to fugitives.

The site is easily accessible near the town center of Mohill and remains partly integrated with the standing church structure. Some ruins are positioned beneath the current church, which limits what can be fully observed at ground level.

The Annals of the Four Masters record that Mohill Priory held the right to grant sanctuary to a fugitive fleeing from enemies, noted for 1430 when Donough Mac Tiernan was driven into the monastery and later came out under Mac Rannall's guarantee to make peace.