Oleanolic acid (3beta-hydroxy-olea-12-en-28-oic acid, OA) exists widely in plant kingdom and possesses various pharmacological activities. In recent years, it was found that it had marked anti-tumor effects and exhibited cytotoxic activity towards many cancer cell lines in culture. In this article, the anti-tumor and differentiation-inducing effects of a derivative of OA modified at C-3, 3-oxo oleanolic acid (3-oxo-olea-12-en-28-oic acid, 3-oxo-OA, 3-7-1) was reported. In vitro, 3-7-1 were found to inhibit significantly the growth of cancer cells derived from different tissues. And 3-7-1 had inhibitory effect on melanoma in vivo. This selection may relate to the differentiation induced by 3-7-1. The inhibition of 3-7-1 on B16-BL6 suggests that 3-7-1 may be a useful anti-cancer agent for melanoma.