To explore the changes of splenic T lymphocyte subsets and functions in mice under high-altitude hypoxic conditions. After mice were exposed to an altitude of 400 m,2200 m and 4200 m for 30 days,ELISA was used to detect the concentrations of interleukin-4( IL-4) and interferon-γ( IFN-γ) in the cultured splenocyte supernatant; MTT assay was used to analyze the proliferation of splenic T lymphocytes; flow cytometry was performed to examine the alterations of splenic T lymphocyte subsets. After exposed to hypoxia for 30 days,in comparison with the control group( 400 m),the spleen index of the mice increased significantly in both the 2200 m and 4200 m groups,and the spleen index of the 4200 m group was apparently higher than that of the 2200 m group; the concentration of IFN-γ in the splenocyte supernatant of the 4200 m and 2200 m groups significantly decreased,while the concentration of IL-4 had no obvious change. The proliferation of splenic T lymphocyte was reduced obviously in both the 2200 m and 4200 m groups,at the same time,the proliferation of T cells in the 4200 m group was markedly lower than that in the 2200 m group. The percentages of splenic CD3~+,CD4~+and CD8~+T lymphocytes decreased markedly in the 2200 m and 4200 m groups,among them,the number of CD4~+T cel s decreased significantly than CD8~+T cel s. In addition,CD3~+and CD4~+T lymphocyte percentages of the 4200 m group obviously decreased compared with the 2200 m group. In mice exposed to hypoxia at an altitude of 4200 m and 2200 m for 30 days,the number of T lymphocyte subsets and the proliferation ability of T cel s decrease,and the level of IFN-γ is decreased as well.