OBJECTIVE: To investigate the positive rate of hepatitis B surface antibody (HBsAb) in children. METHODS: Blood samples from 3022 children who received a physical examination in outpatient departments from 2009 to 2011 were subjected to serological test using ELISA to measure the positive rate of HBsAb. RESULTS: The positive rate of HBsAb decreased with age (P0.05), however the positive rate of HBsAb in boys aged one year and over was lower than in girls of the same age (P<0.01). The positive rate of HBsAb in boys aged between 3 and 4 years was higher than in girls of the same age (P<0.01). The positive rate of HBsAb decreased with age in boys, and was lower in those aged two years and over than in those aged one year and over (P<0.01). The positive rate of HBsAb also decreased with age in girls, with significant differences between different age groups (P<0.01). CONCLUSIONS: The positive rate of HBsAb decreases with age in children, so younger children have a higher risk of infection with hepatitis B virus. Serological monitoring of hepatitis B needs to be enhanced.