 The study population in this study is composed of patients who have chronic hepatitis B and achieved HBsAg loss from interferon treatment. Eligible patients will have serum HBsAg and HBV DNA tests every 3 months for 96 weeks after finishing the interferon treatment. The sustained HBsAg response is defined as the levels of serum HBsAg mantaining below the low level of quantitation and the levels of HBV DNA remain undetectable. Following the completion of the study period, patients will be offered to participate in a long term study for further observation up to 240 weeks. 