213 LACA mice were irradiated respectively with dose of 2.5,4.0, 5.5 and 7.0 Gy γ-rays and sacrificed within 4 weeks after radiation. By means of light and electron microscopy, in situ terminal labeling and biochemical analysis apoptotic hematopoietic cells apoptosis were investigated in irradiated mouse bone marrow. The results showed: Much more apoptotic cells were found in each irradiated group bone marrow at 6 h after radiation. Furthermore, the higher radiation dose was, the more apoptotic cells were. The characteristics of apoptotic cells were the chromatin condensation and margination, just as half-moon,ring-like or irregular shapes. The nucleus may be break up and became apoptotic bodies. There was DNA degradation of apoptotic cells detected by in situ terminal labeling and DNA ladder formation in agarose gel electrophoresis. Conclusion: At the range of 2.5 to 7.0Gy irradiation,apoptosis is the main pathway for radiation-induced hematopoietic cells death.