Abstract: ObjectiveTo evaluate the role of CT scan,SOD and MDA expression in radiation lung injury. Methods The right hemithorax of SD rats were irradiated with a single dose of 7.0 Gy and 14.4 Gy. All animals were sacrifaced and the lung were removed at 1,7,30,90 days after radiation. The specimens were stained with HE,Masson to observe the histopathological changes.And the expression of SOD and MDA in serum by ELISA. ResultsThere were no notable hispathological changes in control groups and 7.0 Gy group. Otherwise,the formation of fibrosis could be observed in 14.4 Gy group. CT scan showed no significant opacities in the control group and 7.0 Gy group. However,there were scattered patchy of high intensity in the radiation field in 14.4 Gy group after radiation. Compared with the control group,the expression level of SOD and MDA had no significant difference in 7.0 Gy group at all time points. After 14.4 Gy exposed,The level of SOD was increased at 1 day and decreased at 30,90 days. The level of MDA was significantly elevated at 1day and remained high level at each time point. ConclusionMore than “threshold” dose of radiation，the image changes had occur in lung tissue,there had some clinical value,but the predictive effect of CT scanning was delayed,because image changes often occur after pathological physiological changes. Compared with SOD,the expression of MDA not only could be tested in blood but also was relatively stable which showed that it played an important role to predict the radiation-induced lung injury.