Abstract: Objective: To investigate the effects of simulated weightlessness on intercellular adhesion molecule-1（（ICAM-1）） in serum and pulmonary tissues in rats.Methods: -30° tail-suspension（TS） rats were used as the model to simulate the physiological effects of weightlessness.40 Wistar male rats were randomly arranged into 4 groups: control for 7 d（7 d CON）,21 d CON,TS for 7 d（TS7 d） and TS21 d.The dynamic expresses of ICAM-1 in the sera and lung tissues were respectively observed by using ELISA and the immunohisochemical technique.Results: The ICAM-1 express was not detected in sera among all groups.The activation level of ICAM-1 in the lung tissue of TS7d rats increased highly significantly,and did slightly in TS 21 d（P＜0.01）.Conclusion: TS resulted in some lung injury of rats,which could have some effects on the pulmonary circulation and function.