In order to establish the stable clones of RAW264.7 cells with S100A8 gene overexpression, and directly investigate the role of S100A8 in γ-rays induced hematoiesis/immune system injury, RT-PCR method and immuno-fluorescence staining analysis were performed to measure the expression of S100A8 mRNA and protein. The cell cycle was detected by flow cytometry at 6 h after irradiation with 10 Gy γ-rays. The level of reactive oxygen intermediates (ROIs) was detected by flow cytometry at 6h after H,2,O,2 ,treatment. The cell cycle analysis showed that the percentages of RAW264.7/S100A8 cells had an increase in G,0,/G,1, phase and a decrease in S phase, and G,2,/M arrest didn’t occur in experimental group while the level of ROIs was lower than that of the negative control cells. These results indicate that radiation resistant of RAW264.7/S100A8 cells may be related to the antioxidant role of over-expressed S100A8 in comparison to RAW264.7/pcDNA3.1+ cells.