Objective:To investigate the relationship between serum IL-10 and apoptosis of T lymphocytes in systemic lupus erythematosus(SLE). Methods:ABC-ELISA was used to analyze the level of serum IL-10. Three-color flow cytometry was used to determine the changes of percentages of peripheral T lymphocyte subsets,their expressions of Fas and FasL,and of their early apoptosis. And then,the relationship between these changes and the level of serum IL-10 was analyzed. Results:In SLE,compared with normal controls,the serum IL-10 level increased significantly,and had a positive correlation with SLEDAI and the level of serum anti-dsDNA antibodies. In peripheral blood,the percentage of CD4+ cells and CD4+/CD8+ ratio was decreased,and the expression rates of Fas and FasL of T lymphocyte subsets was increased. The early apoptosis of T lymphocyte subsets,especially of CD4+ subpopulation,was increased. These results above became more obvious in SLE patients with active disease. In SLE,there was a negative correlation between serum IL-10 level and CD4+/CD8+ ratio,while a positive correlation between serum IL-10 level and the increased expression of FasL, and the increased apoptosis of CD4+ T lymphocyte. Conclusion:The abnormally increased serum IL-10 level in SLE patients can induce a high level of FasL,which mediates the apoptosis of CD4+ T lymphocyte,and involves in a more active disease.