The Feeding habits of the purple sea urchin around the coast of Dalian was investigated. The results show that mature sea urchin in natural sea area mainly feed on algae and small animals, among which Laminaria japonica and Ulva pertusa occur frequently The food taken by sea urchin is greatly related to their living surroundings. If food is rich, the urchin will make its choice.The pre-ferential order about algae are Undaria and Laminaria in Phaeophyta, Chondrus and Gelaclium in Rhodophyta and Ulva and Enteromorypha in Chloraphyta.Some animal food are also taken by the sea urchin. Therefore the feeding habits of S.nudus is omnivorous.