By using the models of tumor blood-borne metastasis and spontaneous one, the antitumor metastasis effect of 75 mGy X-ray whole body irradiation on tumor bearing mice is investigated. The results demonstrate that irradiation could significantly inhibit B16 melanoma blood borne pulmonary metastases (P <0.05) and Lewis lung carcinoma (LLC) spontaneous pulmonary metastases (P <0.01). The immunofunction test of B16 melanoma bearing mice shows that the NK (P <0.05) and LAK (P < 0.001) cytotoxicities, and responsibility of splenocytes to 1L-2 (P < 0.005) for the irradiated group are increased greatly compared with those of control group. These results suggest that the enhancement of immunofunctions is induced by low dose radiation to raise antitumor metastasis effects.