Abstract: The aim of the study was to compare the morphological characteristics and antioxidant capacity of lung tissue between one year old and adult Black Tibetan sheep. Five healthy male Black Tibetan sheep aged 12 months and 24 months were selected from Guinan County, Haibei Prefecture, Qinghai Province under natural grazing condition, repectively. The sheep were divided into two groups according to the age of month: one year old sheep group（12 months） and adult sheep group（24 months）. Two right lung septum samples were collected from sheep after slaughter of the two groups, one of whose morphology of lung tissue was observed by H.E. staining microscope, the other one of whose alveolar septum thickness, single alveolar area and number of alveoli per unit area were measured by Image-Pro Plus 6.0 Image analysis system, and the diameter and media thickness of pulmonary terminal branches and small arteries were measured. The mean diameter of pulmonary vessels and media thickness/mean vessel diameter of lung tissue were calculated. Meanwhile, the total antioxidant capacity（T-AOC）, the activities of superoxide dismutase（SOD）, catalase（CAT） and glutathione peroxidase（GSH-Px） and the content of malondialdehyde（MDA） in lung tissues of sheep were determined by kit. The results showed that compared with one year old sheep group, the alveolar septum thickness and alveolar number per unit area of adult sheep group were significantly increased（P＜0.05）, while the single alveolar area, mean diameter of pulmonary vessels and thickness of media were significantly decreased（P＜0.05）. The ratio of media thickness to mean vessel diameter was decreased, but the difference was not significant（P＞0.05）. T-AOC and the activities of SOD, GSH-Px and CAT in lung tissue were slightly increased, while the content of MDA was slightly decreased, but the differences were not significant（P＞0.05）. It indicated that with the growth of Black Tibetan sheep’s age, the lung gradually adapted to the plateau low oxygen environment, but the antioxidant capacity did not change significantly.