Abstract: Objective The study investigates the inhibitory role of ursolic acid on COX-2 expression of human gastric cancer cells SGC-7901. Methods The anti-proliferation effect of ursolic acid towards SGC-7901 and effect of exogenous prostaglandins E2 on cell proliferation were determined by MTT assay; Western blot assay was used to determine expression of COX-2 protein; The effect of ursolic acid on PGE2 production in SGC-7901 cells were determined by radioimmunoassay（RIA）. Results Ursolic acid could inhibit the proliferation of SGC-7901 cells in a time-response and concentration-response manner; This role could not be invert in the presence of exogenously added prostaglandin E2; COX-2 protein level was decreased by ursolic acid and then PGE2 production was inhibited. Conclusions Our findings indicate that ursolic acid inhibit the proliferation of SGC-7901 by inhibits COX-2 protein and PGE2 expression, suggest a possible mechanism for its chemopreventive and anticancer effects.