Abstract： Objective To analyze the characteristics of immunocompetent cells in peripheral blood on prophase of severe hepatitis B (PSHB).Methods 48 cases of PSHB patients,35 cases of chronic hepatitis B(CHB) patients and 20 cases of healthy volunteers were enrolled for detection of CD3+,CD3+/CD4+,CD3+/CD8+ and CD4+/CD25+/CD45+ lymphocyte subsets in peripheral blood by flow cytometry.The absolute numbers of each lymphocyte subset were calculated and analyzed statistically.Results Compared with CHB group and healthy control group,The absolute numbers of circulating CD3+,CDs+ T cells and CD4+ CD25 + regulatory T cells (Tregs) were significantly lower in PSHB group( P ＜0.01 or P ＜0.05).There was no significant difference on the absolute numbers of circulating CD4+ T cells betweenPSHB group and CHB group (P ＞0.05),while the percentage of lymphocyte subsets CD4+ in PSHB group was significantly higher than that in CHB group( P ＜ 0.05 ).In addition,CD4 +/CD8 + ratio in PSHB were significantly higher than those in the CHB group and healthy control group ( P ＜ 0.01 or P ＜ 0.05 ).Conclusion PSHB has a certain degree of cellular immune dysfunction,which characterized by CD4+ T cells dominated and the decline of absolute numbers of CD8 + T cells and CD4 + CD25 +Tregs.