Abstract: Objective To investigate the minimum age of hepatitis B virus(HBV)surface antibody(HBsAb)attenuation among the children with basic hepatitis B vaccination at the age of 0,1,and 6 months and to provide a scientific basis for making immunization strategy.Methods Totally 2 026 children aged ≤ 7 years visiting a healthcare clinic for routine physical examination were recruited from January 2011 through December 2014 and serum markers of HBV infection were detected among the children with enzyme-linked immunosorbent assay(ELISA).Model fitting was adopted to analyze associations of median age and real age with positive rate of HBsAb for the children of different age groups for estimating the minimum age for HBsAb attenuation.Results Of the children,2.72%(60)had HBV infection of different period as described by 14 expressions of model 1 to model 14;28.51%(629)were negative for HBsAb and susceptible to HBV infection(model 15);68.77%(1 517)were positive for HBsAb and unsusceptible to HBV infection(model 16).Among the 2 146 children without HBV infection,the positive rate of HBsAb was 70.69%and no significant between-gender difference in the rate was observed(P>0.05).The lowest HBsAb positive rate(49.52%)was observed among the children aged 4.0-4.5 years.The estimated minimum median age and actual age for HBsAb attenuation were 3.99 and 4.01 years,respectively,based on the results of model fitting.Conclusion The study results suggest that serological markers of HBV should be tested at the age of 4 years among the children with basic vaccination of three doses for the implementation of supplementary HBV vaccination.