Cisplatin (CDDP) is widely used to treat several types of cancer. However, CDDP induces nephrotoxicity. This toxicity could be avoided, applying a lower cisplatin dose; however, it could induce a lesser therapeutic activity. In this paper, we present the cytotoxic activity against prostate human cancer cell line (PC-3) of the combination of CDDP with masticadienonic acid (MDA), a triterpene isolated from Amphypterygium adstringens.The combinations A (half of the IC50), B (IC50) and C (twice IC50 of the compounds) in a radio 1:1 were evaluated. Our results showed that the B and C combinations presented synergism effect. However, B combination showed almost 100% inhibition of cell proliferative activity and increased apoptosis compared with those presented by each compound apart. A pretreatment of MDA 24 h to cells before the CDDP, AMD or B combination administration result in a resistance to the treatments. A xenograft study using PC-3 cells showed that the combination of 47.5 mM/kg (AMD) plus 4 mM/kg (CDDP) administered weekly for 3 weeks reducing the tumor volume in approximately 47 %. However, the combination of 47.5 mg/kg (AMD) plus 2 mg/kg (CDDP) administered every third day for 21 days reduce, approximately 82% of tumor compared with mice no treated.