Saint Piran's Chapel is a long, single storey slate construction in the hamlet of Trethevy in the parish of Tintagel, Cornwall, UK.

A stone coffin was found in July 1944 by Father Edward Arundell, vicar of Tintagel.

It is unclear why there should be a chapel dedicated to Saint Piran so far from the concentration of places associated with him to the west of the county but the Domesday Book mentions the ‘monks of St. Pieran’ who owned the manor of Tregrebri in this part of Cornwall (this can plausibly be identified with Tregenver, a farmstead near Trethevy).

Other chapels bore St.Piran's name, including that according to Giraldus Cambrensis standing in the road in front of Cardiff Castle where Henry II was the recipient of a vision precluding Sunday markets.

A small lancet window with a trefoil head remains in the east wall and what appears to be a rough stone shelf or piscina is on the south side.