Objective To investigate the protective effects of antitumor necrosis factor-α antibody （TNF-αAb） on lung injury after cardiopulmonary bypass （CPB） and their mechanisms. Methods Forty healthy New Zealand white rabbits，weighting 2.0-2.5 kg，male or female，were randomly divided into 4 groups with 10 rabbits in each group. In groupⅠ，the rabbits received CPB and pulmonary arterial perfusion. In group Ⅱ，the rabbits received CPB and pulmonary arterial perfusion with TNF-αAb. In group Ⅲ，the rabbits received CPB only. In group Ⅳ，the rabbits only received sham surgery. Neutrophils count，TNF-α and malondialdehyde （MDA） concentrations of the blood samples from the left and right atrium as well as oxygenation index were examined before and after CPB in the 4 groups. Pathological and ultrastructural changes of the lung tissues were observed under light and electron microscopes. Lung water content，TNF-α mRNA and apoptoticindex of the lung tissues were measured at different time points. Results Compared with group Ⅳ，after CPB，the rabbitsin group Ⅰ to group Ⅲ showed significantly higher blood levels of neutrophils count，TNF-α and MDA（P＜0.05），higherTNF-α mRNA expression，apoptosis index and water content of the lung tissues （P＜0.05），and significantly lower oxyg-enation index （P＜0.05） as well as considerable pathomorphological changes in the lung tissues. Compared with group Ⅱ，after CPB，the rabbits in groups Ⅰ and Ⅲ had significantly higher blood concentrations of TNF-α （5 minutes after aortic declamping，220.43±16.44 pg/ml vs.185.27±11.78 pg/ml，P＜0.05；249.99±14.09 pg/ml vs.185.27±11.78 pg/ml，P＜0.05），significantly higher apoptosis index （at the time of CPB termination，60.7‰±13.09‰ vs. 37.9‰±7.78‰，P＜0.05；59.6‰±7.74‰ vs. 37.9‰±7.78‰，P＜0.05），significantly higher blood levels of neutrophils count and MDA （P＜0.05），significantly higher TNF-α mRNA expression and water content of the lung tissues （P＜0.05），and significantly loweroxygenation index （P＜0.05） as well as considerable pathomorphological changes in the lung tissues. Compared with groupⅠ，rabbits in group Ⅲ had significantly higher above parameters （P＜0.05） but lower oxygenation index （P＜0.05） only at 30 minutes after the start of CPB. Conclusion Pulmonary artery perfusion with TNF-αAb can significantly attenuate inflammatory lung injury and apoptosis of the lung tissues during CPB.