Background Regulatory T cell populations,particularly cD4+CD25* T regulatory cells,have been implicated in the persistence of hepatitis B virus (HBV) infection.However,no clear relationship has been established between the frequency of CD4*CD25+ T regulatory cells in the peripheral blood and either the disease phases in the natural history of chronic HBV infection or in the response to interferon-α therapy.Methods In the present study,three different common markers of CD4+CD25+ T regulatory cells were used to determine the numbers of T regulatory cells in healthy controls and in patients with chronic HBV infection.Results No significant difference was found when samples were gated for CD25hi and CD25+FoxP3+ T cells.A significant correlation was found between the number of CD4+ Treg cells that gated with CD25+FoxP3+ and CD25+CD127low/- in healthy controls and in patients with chronic hepatitis B (CHB) (r=0.67,0.59; P ＜0.01).The percentages of Treg cells were (8.56±2.01)％ in asymptomatic carriers (Asc),(8.74±3.04)％ in inactive HBsAg carriers,(10.7±2.93)％ in CHB and (7.42±1.28)％ in healthy controls (F=11.1,P＜0.001).The percentage of Treg cells in patients with CHB was higher than in asymptomatic HBV patients,inactive HBsAg carriers,or healthy controls (P ＜0.01).The proportion of CD4+CD25+CD127low/ T cells in patients who responded to interferon-α was (11.9±3.3)％,(9.1±2.4)％ and (9.0±2.9)％ at baseline,week 12 and week 24 after treatment,respectively (Z=2.42,P＜0.05; Z=2.67,P＜0.01).Conclusions These results suggest that the proportion of the CD4*CD25* regulatory T cells might be affected by the application of different markers in process to detect T regulatory cells.The frequency of Treg cells was increased in patients with CHB,which might be associated with the disease activity of these patients and contribute to prevention of extensive liver damage.A decline in Treg cells at week 12 of treatment might be associated with a better response to treatment with interferon-α.