In this paper the radiosensitization of docetaxel on Lewis lung cancer was investigated in vivo. C57BL mice bearing Lewis lung cancer were treated with 207mg/m,2, docetaxel to determine the ability of the drug to induce mitotic arrest and apoptosis in tumor cells. The mice bearing Lewis lung cancer in the right hind leg were locally irradiated with single dose of 10Gy ,137,Cs γ rays using small animal irradiator. The results showed that the percentage of arrested cells increased rapidly with the time,achieving its peak of 31.9% 12h after docetaxel administration. Docetaxel also induced apoptosis within 48h. Treated by different doses of docetaxel 12 or 48h prior to irradiation,the tumors grew slowly,the growth inhibition rates of the tumors increased, and the relative growth rates decreased significantly. The q value in every radiosensitizing group ranged from 1.21 to 1.38. These results indicated that docetaxel exerted its radiosensitizing potential by the mechanism of arresting mitosis and inducing apoptosis. This study suggested that docetaxel had a high potential as a successful radio sensitizer in the clinic treatment of lung cancer.