Abstract: Objective To investgate the relationship among the plasma ET-1 levels at pre-、 treatment 40Gy and posttreatment stages. Lung Dose-Volume Histogram Parameters V20 and radiation-induced lung injury. Methods Forty-eight non-small cell lung cancer patients receiving 3DCRT were included in this study.The radiation was delivered in 2Gy per fraction,5 fractions per week with the total dose ranging plasma ET-1 at 62~66Gy.The percentage of both lung volume receiving 20Gy or more(V20）was retricted to 30% or less, and the dose of spinal cord was retricted to 45Gy.We use the methods of ELISA to quantitate the concentration of among pre-, 40Gy and posttreatment stages. Results The totle radiation-induced injury was noted among 27.1%（13/48） of patients.The incidence of the radiation induced lung injury was 41.7% among patients with ET-1 levels elevated when received 40Gy,and this was significantly higher than those with normal ET-1 levels (12.5% ) （P=0.023).The incidence of the radiation-induced lung injury was 44% among patients with elevated posttreatment. ET-1 levels were significantly higher than those with normal ET-1 levels (8.7%)（P=0.006). The radiation-induced lung injury developed in 69.2% of patients with V20≥25% and elevated post-treatment ET-1 levels,and this was significantly higher than those of other groups.Those patients with V20＜25% and normal post-treatment ET-1 levels have 5.9％ developped radiation-induced lung injury,which was significantly lower than those of other groups. Conclusion Radiation-induced lung injury is significantly related to the concentration of plasma ET-1 during and afterradiotherapy. Patients with V20≥25% and elevated posttreatment ET-1 levels are at especially high risk to develop radiation-induced lung injury.It may be regarded as a factor to predict radiation-induced lung injury and is worthy of clinical generalization and further clinical observation.