Portencross Castle, also known historically as Portincross Castle, is situated in Portencross, on the west coast of Scotland, about 3 km from West Kilbride. The site has been fortified since the 11th Century. The present tower castle is thought to date from the mid-14th Century and later. It remained in use until it was unroofed by a great storm in 1739 and gradually became ruinous. The castle was designated as a scheduled ancient monument in 1955.
The castle was one of the buildings featured in the 2004 series of the BBC television programme Restoration and was the subject of efforts by a local community group to secure its future.