Objective To assess on-treatment serum HBsAg and HBV DNA kinetics in HBeAg-positive CHB patients to predict the efficacy of pegylated interferon(PEG-IFN) in early phase of treatment. Methods Forty-one treatment-naive HBeAg-positive patients treated with PEG-IFNα 2a at a dose of 180 μg/week for at least 24 weeks were evaluated. Their treatment response was assessed, including normalization of serum ALT, decline of serum HBV DNA and loss of HBeAg. Results We found that a decrease of HBV DNA level at the 4th week was positively correlated with the decrease of HBV DNA level at the 12th week and 24th week(r = 0.8202, P < 0.0001 and r = 0.6838, P < 0.0001, respectively). We observed that a decrease of HBsAg level at the 4th week was positively correlated with decrease of HBsAg level at the 12th week and 24th week(r = 0.4868, P = 0.0023 and r = 0.4251, P = 0.0109, respectively). A decrease of HBsAg level at the 24th week was positively correlated with the decrease of HBV DNA level at the 24th week(r = 0.5262, P = 0.0024). Serum level of IFN and IFN neutralizing antibody had no relationship with HBV DNA or HBsAg titers kinetics. Conclusions The decline of serum HBV DNA and hepatitis B surface antigen at the 4th week can be used to predict the response to PEG-IFNα 2a in patients with HBeAg positive chronic hepatitis B. Objective To assess on-treatment serum HBsAg and HBV DNA kinetics in HBeAg-positive CHB patients to predict the efficacy of pegylated interferon (PEG-IFN) in early phase of treatment. Methods Forty-one treatment-naive HBeAg-positive patients treated with PEG IFNα 2a at a dose of 180 μg / week for at least 24 weeks were evaluated. Their treatment response was assessed, including normalization of serum ALT, decline of serum HBV DNA and loss of HBeAg. Results We found that a decrease of HBV DNA level at the 4th week was positively correlated with the decrease of HBV DNA level at the 12th week and 24th week (r = 0.8202, P <0.0001 and r = 0.6838, P <0.0001, respectively). We observed that a decrease of HBsAg level at the 4th week was positively correlated with the decrease of HBsAg level at the 12th week and 24th week (r = 0.4868, P = 0.0023 and r = 0.4251, P = 0.0109, respectively). A decrease of HBsAg level at the 24th week positively correlated with the decrease of HBV DNA level at the 24 Th week (r = 0.5262, P = 0.0024). Serum level of IFN and IFN neutralizing antibody had no relationship with HBV DNA or HBsAg titers kinetics. Conclusions The decline of serum HBV DNA and hepatitis B surface antigen at the 4th week can be used to predict the response to PEG-IFNα 2a in patients with HBeAg positive chronic hepatitis B