Abstract: Objective:To investigate the effects of N-acetylcysteine on changes of cell apoptosis in pulmonary tissues of tail-suspended rats during simulated weightlessness.Methods:Tail-suspension was used as weightlessness simulation.30 Spragno-Dawley male rats were randomly divided into 3 groups:control group,tail-suspension for 7 day group and Nacetylcysteine treatment after suspension group.The condition of cell apoptosis in pulmonary tissues was detected with in situ death detection and the condition of bcl-2/bax mRNA in pulmonary tissues was detected by hybridization in situ.Results:The index of cell apoptosis in pulmonary tissues of rats suspended for 7 days was higher than that of control group（P＜0.05）.The index of cell apoptosis in pulmonary tissues of rats in N-acetylcysteine treatment group was lower than that of suspended for 7 days group（P＜0.05）.The expression of bcl-2/bax mRNA in pulmonary tissues had the corresponding changes.Conclusion:The cell apoptosis rate in pulmonary tissues of rats increases after being suspended for 7 days.N-acetylcysteine could suppress cell apoptosis in pulmonary tissues of rats during simulated weightlessness.