Objective To determine the protein and mRNA levels of interleukin-17 (IL-17) in the peripheral blood of patients with systemic lupus erythematosus (SLE), and to analyze the relationship between IL-17 and disease activity. Methods Twenty-six hospitalized SLE patients and twenty-one normal controls were studied. Plasma protein and mRNA of IL-17 in peripheral blood were measured by ELISA and Real-time RT-PCR respectively. Results IL-17 level and its mRNA level increased in SLE patients compared with that in normal controls. Plasma concentration of IL-17 showed a significant positive correlation with SLEDAI score and anti-dsDNA antibody level, and a significant negative correlation with serum C3 level. Conclusions Plasma IL-17 protein and mRNA expression level in SLE patients increased significantly and had close relationship with disease activity, which might suggest that IL-17 play an important role in the pathogenesis of SLE.