Pensarn Harbour is a small quay situated on the north-east, landward bank of the Afon Artro in Gwynedd, Wales, at the point where the river meanders across flatlands before reaching the sea north of Ynys Mochras (Shell Island).

It lies within the historic parish of Llanfair, between Llanbedr and the coast.

The harbour's current form owes much to a deliberate engineering change: in 1819 the Earl of Winchilsea diverted the Artro to improve access to the wharf, which served as the shipment point for slate from the villages of Llanfair and Llanbedr.

Prior to that diversion, the river had entered the sea to the south of Mochras. The Artro is believed to have once been navigable by small vessels as far upstream as the break of slope near Llanbedr.

Today the site is also home to CMC Adventure, an outdoor education centre, and is served by Pensarn station on the Cambrian Coast Line.