Objective To study the bacteriological effect of different dosages of gamma irradiation on Escherichia Coli (E. Coli) in red blood cells (RBC) products,and assess the appropriate dose of gamma irradiation. Methods Prepare RBC samples inoculated with(102-106)/ml of E. Coli. The contaminated RBCs were irradiated by 0 (as control),15,20,25,30 and 35Gy of gamma irradiation. E. Coli in the RBCs were tested on days 0,7, and 14 after irradiation. Results The quantities of E. Coli changed after irradiation. The RBCs inoculated with less than 103cfu/ml of E. Coli were completely sterilized by 25 Gy irradiation. Conclusion 25 Gy gamma irradiation can eradicate less than 103cfu/ml of E. Coli in the RBC products.