Aim To investigate the immunological activity change of regulatory T cells （Treg） and discuss its significance in the outcomes of patients with multiple organ dysfunction syndrome （MODS） and acute cerebral infarction（ACI）.Methods According to the development of ACI，patients were divided into MODS group（n8）and non-MODS group（n22）. The patients with ACI were further divided into non-survival group （n5） and survival group（n25）based on their outcomes. Healthy volunteers were served as normal control（n30）. Peripheral blood samples were collected in patients with ACI and healthy volunteers. The immunomagnetic separation technique was applied to separate and purify CD4⁺CD25⁺Tregs in peripheral blood，and phenotypes（CTLA-4） were analyzed by flow cytometry and the contents of interleukin-10（IL-10） released in the supernatants were determined by ELISA. Results Expression of CTLA-4 and level of IL-10 were significantly increased in patients with ACI compared with normal control group. The expression of CTLA-4 and level of IL-10 in MODS group were much higher than those in non-MODS group （P<0.01）. Among the ACI patients，the expression of CTLA-4 and level of IL-10 in the survival group were obviously lower than those in the non-survival （P<0.05 or P<0.01）. Conclusion After ischemia reperfusion injury of cerebral，expressions of the markers on CD4⁺CD25⁺Tregs surface and secretion of cytokines produced by CD4⁺CD25⁺Tregs show significant difference in patients with MODS development and survival state. CD4⁺CD25⁺Treg may play an important role in the pathogenesis of immunoregulation，MODS and mortality of patients with ACI through secretion of inhibitory cytokines.