Abstract: Abstract In this paper we observed the chemosensitizing effects on CMNa on some anti-tumor drugs with C₅₇ BL/6and BAL/c mice bearing Lewis, B16 and EMT6 tumors. The results show that relative increasing velocity of tumor was obviously decreased, tumor inhibition rate and the days of tumor growth delay were morely increased when the mice were treated with carboplatin and mitomycin c combined with CMNa than that of anti-tumor drugs treatment alone. But no chemosensitizing effect was observed when the mice were treated with Vp16 combined with CMNa. Those results suggest that the anti-tumor action of some alkylating chemotherapeutic agents (carboplatin, mitomycin c) is enhanced when tumorbearing mice are pretreated with nitroimidazole chemosensitizer (CMNa).