The study explores the expression of calcium-binding protein S100A8 and the relationship between S100A8 and cell cycle or apoptosis in bone marrow cells of mice with radiation injury. The protein/DNA bi-parameter flow cytometry method has been used to analyze the change of S100A8 protein expression and the difference in cell cycle or apoptosis between S100A8 positive and S100A8 negative cells in bone marrow of mice at 6h after irradiation with 3.5 or 7 Gy ,60,Co γ-ray in vivo. In the normal bone marrow of mice, S100A8 positive cells are mainly granulocytes, and they are inactive in cell proliferation compared to S100A8 negative cells. At the early phase of radiation injury, the proportion of S100A8 positive cells and the expression level of S100A8 protein have no significant change in bone marrow of mice; G,2,/M arrest and apoptosis occur in S100A8 negative cells, but no change of cell cycle and apoptosis occur in S100A8 positive cells. These phenomena suggest that S100A8 positive cells in bone marrow of mice are radiation resistant compared to S100A8 negative cells.