Objective To explore the immune mechanism in the systemic lupus erythematosus MRL/ lpr mice at different months of age, and to provide the basis for research of its pathogenesis. Methods 3-, 4-, 5- and 6-month old female MRL/ lpr mice, and wild type C57 female mice were used in this study, 10 mice per each group. Their organ coefficients were determined. ELISA was performed to detect the serum levels of double stranded DNA ( ds-DNA) antibody. The interleukins IL-2, IL-4, IL-17 and tumor necrosis factor-α (TNF-α) in spleen tissue were detected. Flow cytometry was used to assess the content of spleen lymphocyte CD3 cells and CD4/ CD8 cell ratio. Results Compared with the 3-month old wild-type C57 mice, the spleen coefficient, the blood concentration of ds-DNA antibody, IL-2 and TNF-α in the 3- to 6-month old MRL/ lpr mice were significantly increased ( P < 0.05). There was no significant difference between the concentrations of interleukin IL-4 ( P > 0.05). The blood concentration of IL-17 in the 5- and 6-month old MRL/ lpr mice was significantly lower ( P < 0.05 or P < 0.01) than that in the 3-month old MRL/ lpr mice. The rest indexes of MRL/ lpr mice showed no obvious changes or significant difference in the mice at different ages. Compared with the 3-month old C57 mice, the spleen CD3 lymphocyte concentration in the MRL/ lpr mice was significantly decreased ( P < 0.01). With the increasing age, the CD3 lymphocyte concentration and D4 + / CD8 + cell ratio in the MRL/ lpr mice were decreased, however, showing a non-significant difference ( P ﹥ 0.05). Conclusions The data obtained in this study indicate that 3-month old lupus MRL/ lpr mice have already immune injury, increasing with the increase of age of the mice.