Lewis (lung cancer)-bearing C57BL/6 mice and EMT 6 (a mouse mammary carcinoma)-bearing BALB/c mice were fractionally irradiated (8 Gy Per time twice a week, total absorbed dose 64 Gy). In experimental groups radiotherapy protocol was combined with CMNa (0.1,1.0 mmol/kg) or metro nidazole (0.1 mmol/kg). The results showed that, comparing with the untreated tumor, the therapeutic efficacy was observed when tumor was treated with fractionated irradiation and the relative tumor volume was reduced. For EMT 6 tumor metronidazole had some radiosensitizing effect (Fig.2),relative tumor volume was more reduced comparing with radiation alone group, and for Lewis lung cancer there was no radiosensitizing effect was observed. When CMNa was combined, the radiosensitizing effect was obviously enhanced for both tumor models. At the same dosage (0.1 mmol/kg), the radiosensitization of CMNa was higher than that of metronidazole.