Objective To investigate the changes of regulatory T cells (Tregs) in hepatocellular carcinoma(HCC) patients with thermal ablation therapy(TAT),and to explore the mechanisms of immunity enhancement induced by TAT.Methods A total of 36 patients with HCC undergoing TAT (observation group) were enrolled in this study from December 2009 to December 2010.Another 20 healthy person were selected as control group.The percent of Tregs was detected by flow cytometry analysis.The level of serum IL-10 was measured with ELISA.Results Before treatment,the percent of Tregs in TAT group was significantly higher than that in control group [(11.44 ± 2.74)％ vs.(2.45 ± 0.67)％] (P ＜ 0.01).After treatment,the percent of Tregs in TAT group decreased significantly[(11.44 ± 2.74)％ vs.(5.07 ± 0.82)％] (P ＜ 0.01).The level of serum IL-10 in TAT group [(41.66 ± 9.24) mg/L] was significantly higher than that in control group [(14.32 ± 3.64) mg/L] (P ＜ 0.01).After treatment,the level of serum IL-10 in TAT group decreased significantly[(41.66 ± 9.24) mg/L vs.(25.47 ± 5.43) mg/L] (P ＜ 0.01).Conclusion TAT can enhance immunity in HCC patients,and which may accomplish by down regulation of Treg and IL-10.