Objective: To explore the effects of IL-10 on acute leukemic immune evasion. Methods: Plasma concentrations of IL-10 were measured by ELISA in 56 first-visit acute leukemic patients. And expressions of IL-10 on leukemic cells in 30 patients were measured by indirect immunofluorescence technique.Results: Compared with those in control group, IL-10 concentrations increased significantly in first-visit acute leukemic patients. And there was a slight but not significant decrease of IL-10 in patients with acute lymphocytic leukemia(ALL) compared with those with acute non lymphocytic leukemic(ANLL). After intensive chemotherapy,there was a significant decrease of IL-10 in completely remitted(CR) patients ,especially in those with ANLL,but there was still a significant increase compared with those in control group.The positive rate of cells giving out yellow-green bright fluorescence on membranes was 10%-80% ;there were 18 patients expressing IL-10(18/30,60% ) positively :among them 11 with ANLL(11/19,58% ) and 7 with ALL(7/11, 64%) respectively while that of peripheral mononucleate cells in control group was 13%.Compared with that in control group,there was a significant increase of positive rate in ANLL and ALL but with no significant difference between ANLL and ALL. Conclusion: Probably as one of important mechanisms of acute leukemic immune evasion,IL-10 secreted by leukemic cells,contributing to the immunosuppressive state at the tumor site,increase significantly in acute leukemic patients.