Objective:to study the effects of genistein on hematopoiesis and surivial of irradiated mice. Methods: adult male mice were administered orally with genisstein(160mg/kg b.w.) 24h before exposure to a sublethal dose of 6.0gy gamma irradiation. The 30-day survival rate, behavior of hematograms, endogenous hematopoietic spleen colony formation (endocfus), numbers of nucleated cell and granulocyte-macrophage colony forming unit (cfu-gm) in bone marrow following irradiation were examined. In the meantime, protective actions of genistein were compared to those of diethylstilbestrol (des), which was given to mice at dose of 5mg/kg b.w. 24h before irradiation. Results:it was demonstrated that genistein was an effective radioprotector. The survival of irradiated mice protected by genistein was significantly increased and statistically higher than that of mice pre-treated with des. After administration of genistein, enhanced endocfus, numbers of nucleated cell and cfu-gm in bone marrow in mice were found and endocfus numbers was 3.47-fold higher than in irradiated control group. Stimulated recovery of leukocytes, erythrocytes, and thrombocytes were observed in micepre-treated with genistein All above-mentioned results were similar to those in mice protected by des,but the protecting actions of genistein on promoting recovery of nucleated cells and leukocytes were significantly higher than those of des. Conclusion: it could be deduced that the uncertain radioprotective action against death is induced by a possible process of enhanced regeneration of the hematopoietic stem cells due to not only strengthened radioresistance and increased numbers of remained hematopoietic cells, but also enhanced post-irradiation repair or promoted proliferation of the hematopoietic stem cells. These effects of genistein may have some therapeutic implications for radiation-induced injuries.