Objective: To investigate CTLA-4 expression in T cells from peripheral blood of patients with systemic lupus erythematosus （SLE） and its significance in clinic. Methods: Peripheral blood mononuclear cells （PBMCs） from SLE patients and healthy donors were isolated and then cultured with anti-CD3 and anti-CD28 antibodies for 48 hours. Before and after culture， the cells were detected for the percentages of CTLA-4+ cells in CD4+ and CD8+ T subsets by flow cytometry （FCM）. Based on these data， the correlation between CTLA-4 expression in CD4+ or CD8+ T subsets of SLE patients and SLE disease activity index （SLEDAI） and kidney damage were analyzed. Cell culture supernatants were also collected for the determination of free CTLA-4 level by ELISA. Results: In fresh PBMC， CTLA-4+ cell percentages of CD4+CD25+ and CD8+CD25+ T subsets in SLE patients， were significantly higher than those in controls， and were positively correlated with SLEDAI; CTLA-4+ cell percentage of CD8+CD28- T subset was also significantly higher in SLE than that in controls， but was not correlated with SLEDAI. After stimulation with anti-CD3 and anti-CD28， CTLA-4+ percentages of CD4+CD25+， CD8+CD25+ and CD8+CD28- T subsets were significantly lower in SLE than those in controls， but was not correlated with SLEDAI. While in active SLE， CTLA-4+ cell percentage of CD8+CD28- T subsets was significantly lower in patients with kidney damage than that in patients without kidney damage; CTLA-4 level of the culture supernatant was lower in SLE patients than that in controls. Conclusion: The abnormally increased expression of CTLA-4 in T （CD4+ and CD8+） cells fresh isolated from SLE patients T cells might indicate disease development with T cell activation. On the other hand， T cells of SLE patients are deficient in induced expression of CTLA-4， which might be related with the deficient ability of reactivation of SLE T cells in vitro.