Structure of natural product-ursolic acid was modified for increasing its antitumor activity.  Ursolic acid was acylated, esterified, hydrolized or oxidized to obtain target pentacyclic triterpenoid compounds with different substitutes.  Sixteen derivatives of ursolic acid were designed and synthesized including eleven new compounds.  Anti-tumor activities of ursolic acid and these derivatives against HeLa, SKOV3 and BGC-823 cells in vitro were investigated by MTT assay.  The results indicated that compounds 7a and 8a were found to have stronger cell growth inhibitory than ursolic acid on HeLa cells and SKOV3 cells separately, and are worth to be intensively studied further.