Abstract: Objective：To investigate the effects of E838 on mouse survival after lethal dose irradiation and double-strand DNA broken in mouse lymphocyte induced by radiation. Methods ：E838 was given intraperitoneal injection before radiation.The survival time and mortality of mouse were observed.Double-strand DNA broken after 1 Gy γ radiation was detected by single cell gel electrophoresis assay technology and the results was compared with positive drug.The comet image was analyzed by using CASP software and SPSS 12.0 was used for statistical analysis. Results ：The 30d survival time of E838 groups were significantly increased compared with that of control group.Compared with the control group,survival rate in group of E838 with high dose,middle dose and low dose increases by 55 percent,85 percent,75 percent respectively,and it has a significant difference in the survival time(P<0.001).The protective index is 1.99,2.56,2.46 respectively.Compared with Ethinylestradiol, mouse in group of E838 with middle dose and high dose has longer survival time (P<0.001). The double-strand DNA broken in lymphocytes was obviously decreased when mice were preventively given E838 before irradiation.The group of E838 with high dose，middle dose and low dose， the percentage of TDNA（11.68,6.24,9.05）,TL （18.53,10.09,16.02）,TM（2.13,0.64,1.21） and OTM（2.52,0.99,1.59） have a decrease in residual damage(P value<0.001).It has a significant difference among E838,Ethinylestradiol and Nylestriol. Conclusion ：E838 has remarkable protective effects on DNA damage after γ-irradiation.