Quantification of hepatitis B surface antigen(HBsAg)has been suggested to be helpful in the management of chronic hepatitis B(CHB)patients.Nucleos(t)ide analogs(NAs)are the therapy of choice for CHB and are used in the majority of CHB patients.NAs are able to induce hepatitis B virus(HBV)viral suppression,normalization of alanine aminotransferase(ALT)levels,and improvement in liver histology.Automated quantitative assays for serum HBsAg have recently become available,facilitating standardized quantification of serum HBsAg.This has led to increased interest in the clinical application of quantitative serum HBsAg for predicting therapeutic response to NAs.Recent studies have shown that a decline in serum HBsAg levels in patients receiving peginterferon may signal successful induction of immune control over HBV,and can therefore be used to predict therapeutic response.NA treatment typically induces a less rapid decline in HBsAg than interferon treatment;it has been estimated that full HBsAg clearance can require decades of NA treatment.However,a rapid HBsAg decline during NA therapy may identify patients who will show clearance of HBsAg.Currently,there is no consensus on the clinical utility of serum HBsAg monitoring for evaluating patient responses to NA therapy.This review focuses on recent findings regarding the potential application of HBsAg quantification in the management of CHB patients receiving NA therapy. Quantification of hepatitis B surface antigen (HBsAg) has been suggested to be helpful in the management of chronic hepatitis B (CHB) patients. Nucleos (t) ide analogs (NAs) are the therapy of choice for CHB and are used in the majority of CHB patients. NAs are able to induce hepatitis B virus (HBV) viral suppression, normalization of alanine aminotransferase (ALT) levels, and improvement in liver histology. Automated quantitative assays for serum HBsAg have recently become available, This has led to increased interest in the clinical application of quantitative serum HBsAg for predicting therapeutic response to NAs. Recentlycent studies have shown that a decline in serum HBsAg levels in patients receiving peginterferon may signal successful induction of immune control over HBV, and can therefore be used to predict therapeutic response. NA treatment typically induces a less rapid decline in HBsAg than interferon treatment; it has been estimated that full HBs Ag clearance can require decades of NA treatment. Even, a rapid HBsAg decline during NA therapy may identify patients who will show clearance of HBsAg. Current, there is no consensus on the clinical utility of serum HBsAg monitoring for evaluating patient responses to NA therapy. This review focuses on recent findings regarding the potential application of HBsAg quantification in the management of CHB patients receiving NA therapy.