Structural modifications were performed on the C-3 and C-28 positions of ursolic acid and oleanolic acid and the NO production inhibitory activities of the resulting derivatives were evaluated. The SAR revealed that the ursolic acid and oleanolic acid derivatives 3a and 4a, which possessing methoxy group at C-3 position exhibit improved NO production inhibitory activity on LPS-induced RAW247 cells while showing less cytotoxicity than the parent compounds.