the study population in this study were composed of patients who had chronic hepatitis B and achieved HBsAg level≤100 IU/ml with undetectable HBV DNA level after interferon treatment, and serum HBsAg and HBV DNA would be tested every 3 months for 96 weeks after finished treatment. Sustained viral response defined as serum HBV DNA maintaining undetectable during the observation period. HBsAg loss is defined as HBsAg level reached the value lower than the low limited value.