Rosserk Friary, Franciscan friary in County Mayo, Ireland

Rosserk Friary is a ruined Franciscan friary on the west side of Killala Bay, County Mayo. Its church has a single-aisle nave, a bell tower between nave and chancel, and two chantry chapels in the south transept. The conventual buildings retain three vaulted rooms on each side, with two back-to-back fireplaces on the upper floor.

Rosserk Friary was founded in 1441 or earlier for the Franciscan Third Order Regular, in the Diocese of Killala. A papal letter of 14 December 1441 refers to a tertiary of Rosserk, and approval for Rosserk and two other houses was granted by Pope Eugene IV on 23 February 1442. The house was suppressed around 1578 and burned in 1590 by troops of Sir Richard Bingham.

The friary was founded for the Franciscan Third Order Regular, whose members supported local parish priests rather than preaching independently. A carved Round Tower, two angels and the instruments of the Passion survive on a pillar of the double piscina in the chancel's south-east corner. The friary's name, Mainistir Ros Eirc, is Irish.

The site is freely accessible and the stone ruins are laid out in the open for visitors to explore. Sturdy footwear is advisable since the ground is uneven and there are multiple levels to navigate.

Two original fireplaces still stand back-to-back in the upper rooms, revealing how monks heated their living spaces during medieval times. Such paired chimneys are uncommon finds in ruins across the region.