Objective:To study the apoptosis of bone marrow hematopoietic cells and Fas expression in 60Coγ irradiated mice. Methods: Mice were whole-body-irradiated with 4.0 Gy γ-rays.The bone marrow hematopoietic cells were analyzed by electron microscopy(EM),electrophoretic analysis of DNA and flow cytometry. Results:EM showed that there were nuclear contraction and chromatin condensation.Agarose gel electrophoresis of DNA showed ladder pattern.The peak percentage of apoptotic cells occurred 8 h after irradiation. Fas expression significantly increased in bone marrow hematopoietic cells than that of control group 4 h after irradiation. Conclusion: The results indicate that apoptosis occurs in bone marrow hematopoietic cells of mouse with γ-irradiation.The expression of Fas may play a role in raidation-induced apoptosis of hematopoietic cells.