Abstract: Objective : To observe the pathological changes of radiation-induced mouse lungunder hypoxia. Meth-ods : One hundred and forty-four mature mice were divided into two groups: control and hypoxia radiation in which the mice inhaled 10.5% oxygen gas mixture two minutesbefore irradiation to the end of radiation. Each mice lying on back, 2cmx3cm radiation field overthe whole thorax was radiated with 8MV X-ray. The radiation dose were 3,6, 9,12,15 and 18Gy,respectively. The mice were sacrificed on the first ,seventh and twenty-eighth day after the radia-tion. The mouse lung in each group were studied by light-microscopy. Results : The pathological changes of mouse lung in the hypoxic group were milder than that in the control group. Con-clusion : The 10.5% oxygen hypoxia mixture can reduce the radiation damage in mouse lung.