Psilocybe samuiensis is a species of psychedelic mushroom in the family Hymenogastraceae, which has psilocybin and psilocin as its main active compounds.

It has been found in Koh Samui, a small tropical island in Thailand, where some psychoactive species are consumed by both natives and tourists.

Psilocybe samuiensis was first picked in soil containing mixtures of sand and clay west of the village of Ban Hua Thanon, in Koh Samui.

Since then it is now known to occur in Ranong Province in Thailand and also at Angkor Wat in Siem Riap, Kampuchea; and verified by Gaston Guzman.

It grows scattered to gregarious in rice paddies, but never directly on manure, fruiting from early July to late August.