Objective To study the correlation between the percentage of intrahepatic regulatory T cell (Treg) and liver inflammatory activity in chronic hepatitis B (CHB) patients.Methods Twenty-six cases of CHB patients admitted to First Department of Internal Medicine,Nagasaki University School of Medicine,Sakamoto,Nagasaki,Japan were enrolled and performed liver biopsy in this study.CD3+cell and Foxp3+ cell in liver were detected by immunohistochemistry.the percentage of Foxp3+/CD3+cell was determined.Clinical data including alanine aminotransferase (ALT).aspartate aminotransferase(AST), hepatitis B virus (HBV) DNA level and the inflammatory activity of histological activity index score (HAD of liver pathology using Knodell evaluating system were collected.The data was analyzed by SPSS 13.0 software.Results Foxp3+Tregs in serial sections of CHB accumulated mainly in the portal area.There Was a significance correlation between the percentage of Foxp3+/CD3+ cell and liver parenchyma inflammation (P=0.007 6).Moreover,Foxp3+Treg in CHB patients with high serum ALT or AsT level presented in a higher frequency than in patients with low AIT or AST level.The difference between these tWO groups was statistically significant (rALT=O.438,PALT=0.025; fAST=O.436,Past=O.026).There Was a tendency between the percentage of Foxp3+/CD3+ cell in liver and HBV DNA level.however the correlation was not statistically significant.Conclusion It is suggested that CD4+ CD25+ Foxp3+Treg may play a major role in the pathogenesis of liver injury in the CHB patients.