ObjectiveTo investigate the characteristics of circulating CD4+CD25+ regulatory T cells (Treg) in chronic hepatitis B (CHB) patients accepting peginterferon alfa2a and adefovir  therapy. MethodsPeripheral blood mononuclear cells (PBMC) of 35 patients with CHB were collected at baseline and week 12, 24 and 48 treatment. Eighteen patients were treated with peginterferon alfa2a (40 KD) (PEGASYS) and 17 patients were treated with adefovir dipivoxil (ADV). Twelve healthy volunteers with normal liver function and negative hepatitis virus markers were as controls. The proportion of CD4＋CD25＋Treg/PBMC were analyzed using flow cytometry. The correlation between Treg and serum alanine transaminase(ALT) or HBV DNA was also analyzed. ResultsThe proportion of Treg/PBMC in PEGASYStreatment group and ADVtreatment group before treatment were (3.72±1.15)% and (3.63±1.02)% respectively, which were significantly higher than that(2.47±0.90)%  in healthy controls (t=2.51, 2.48; both P<0.05). In PEGASYS group, the proportion of CD4＋CD25＋Treg at week 12, 24 and 48 treatment were (2.87±0.76)%, (2.75±0.72)% and (2.51±0.69)% respectively, which significantly decreased than that of baseline (t=2.41,2.58,2.95; P<0.05, <0.05, <0.01). No significant changes in CD4＋CD25＋Treg were found in ADVtreatment group before and after treatment(P>0.05). A strong correlation was observed between the change in ALT level and the proportion of CD4＋CD25＋Treg (r=0.52, P<0.01). No correlation was found between the change  in HBV DNA and CD4＋CD25＋Treg(r=0.25, P>0.05). ConclusionThe level of peripheral blood CD4＋CD25＋Treg in CHB patients is higher than that in healthy controls. PEGASYS antiviral treatment can decrease the proportion of CD4＋CD25＋Treg, while ADV antiviral treatment has no influence on CD4＋CD25＋Treg.