Portencross (Port na coise) is a hamlet near Farland Head in North Ayrshire, Scotland. Situated about 3 km west of Seamill and about 2 km south of Hunterston B nuclear power station, it is noted for its castle.
It has two harbours and a pier. The "Old Harbour" is actually a small tidal inlet next to the castle, and is part of the castle property. The larger harbour, "North Harbour", owned by the Portencross Harbour Trust, lies about 100 m north of the castle and was the main access point for fishing activity.