Rathfriland Castle () is a ruined castle at Rathfriland, County Down, Northern Ireland. The castle was a square building of 3–4 storeys with a stone barrel vault at the first floor level to reduce the risk of fire and was one of the seats of the Magennis's, Lords of Iveagh. Most of it was pulled down by Mr. William Hawkins of London, after the rebellion of 1641, and the remainder destroyed by General Henry Ireton on Oliver Cromwell's orders.