Objective To evaluate the effects of continous blood purification(CBP) on immune system in patients with multiple organ dysfunction syndrome (MODS). Methods Twenty patients with MODS, were enrolled in this study. All patients underwent CBP for 72 hours. The blood sample was collected from those patients at 0,24h,48h,and 72h during CBP. The monocytes in blood sample were isolated, and incubated with LPS at a concerntration of 10μg/ml for 12hrs at 37℃. The levels of TNF-α、IL-6 and IL-10 in the supernatants were determined by ELISA. The antigen presenting function represented by HLA-DR expression was detected by flow cytometry analysis.The number of cytokines secreted were evaluated in blood. Results ① The secretion function of monocytes: Before CBP, cytokines secreted from monocytes were higher than after CBP, there was a significant reduction of cytokines (TNF-α、IL-6、IL-10) secreted from monocytes after CBP (P<0.05); ② Compared with normal individuals, the HLA-DR expression on monocytes in MODS patients was significantly lower (P<0.01). After CBP the HLA-DR expression was significant improved;③ The number of monocytes :There was a significant decrease of the monocytes number compared with normal before CBP lower monocytes were ameliorated significant by CBP therapy. After CBP treatment, there was a significant reduction of plasma levels of TNF-α and IL-6 in MODS patients; ④ There was a significant increase of plasma level of IL-10 and significant decrease of HLA-DR expression in the 3 cases of died patients. After CBP, there weren't any improvement in the three cases of died patients. Conclusion: ① The abnormalities of immune system in patients with MODS can be improved after CBP therapy; ② The level of IL-10 and HLA-DR as indicators of immune system in MODS patients may be useful; ③ CBP therapy show significant affection in MODS patients with higher immune and higher secreted cytokines.