The paoer is to elucidate radiobiological charicateristics and radiobiological mechanism in killing tumor cells with low dose rate β−rays and high dose rate γ-rays. HeLa cells were exposed to low−rate β−irradiation of ,32,P or high−dose−rate γ−irradiation of ,60,Co. Cell response−patterns were compared between two the types of radiations in terms of their inhibition of cell proliferation and cell cycle blockage, evaluated by typanblue excluded method and flow cytometry, respectively. Results show that there is a different way in growth inhibition effect on HeLa cells between low−dose−rate irradiation of ,32,P and high−dose−rate irradiation of ,60,Coγ. In exposure to ,32,P, the inhibition of cell proliferation in HeLa cell was a prolong course, whereas and the effect was in a more serious and quick way in ,60,Co irradiation. Cell cycle arrest in G,2, phase induced by ,32,P was lower and more prolong than that induced by ,60,Co. The inhibition effect on tumor cells between the two types of radiations is different. Impaired DNA repair system by continuous low−dose−rate radiation might contribute to the final radiation effect of ,32,P.