Background:Hepatitis B surface antigen (HBsAg) loss/seroconversion is considered to be the ideal endpoint of antiviral therapy and the ultimate treatment goal in chronic hepatitis B (CHB).This study aimed to assess the patts of HBsAg kinetics in CHB patients who achieved HBsAg loss during the treatment of pegylated interferon (PEG-IFN) α-2a.Methods:A total of 150 patients were enrolled,composing of 83 hepatitis B envelope antigen (HBeAg)-positive and 67 HBeAg-negative patients.Patients were treated with PEG-IFN α-2a180 μg/week until HBsAg loss/seroconversion was achieved,which occurred within 96 weeks.Serum hepatitis B virus deoxyribonucleic acid and serological indicators (HBsAg,anti-HBs,HBeAg,and anti-HBe) were determined before and every 3 months during PEG-IFN α-2a treatment.Biochemical markers and peripheral blood neutrophil and platelet counts were tested every 1-3 months.Results:Baseline HBsAg levels were 2.5 ± 1.3 log lU/ml,and decreased rapidly at 12 and 24 weeks by 48.3％ and 88.3％,respectively.The mean time to HBsAg loss was 54.2 ± 30.4 weeks,though most patients needed extended treatment and 30.0％ of HBsAg loss occurred during 72-96 weeks.Baseline HBsAg levels were significantly higher in HBeAg-positive patients (2.9 ± 1.1 log IU/ml) compared with HBeAg-negative patients (2.0 ± 1.3 log IU/ml;t =4.733,P ＜ 0.001),but the HBsAg kinetics were similar.Patients who achieved HBsAg loss within 48 weeks had significantly lower baseline HBsAg levels and had more rapid decline of HBsAg at 12 weeks compared to patients who needed extended treatment to achieve HBsAg loss.Conclusions:Patients with lower baseline HBsAg levels and more rapid decline during early treatment with PEG-IFN are more likely to achieve HBsAg loss during 96 weeks of treatment,and extended therapy longer than 48 weeks may be required to achieve HBsAg loss.