Objective To investigate whether maternal antibody to hepatitis B surface antigen (anti-HBs)in infants may interfere with the antibody response to hepatitis B vaccine. Methods Infants from singleton pregnant mothers,who delivered at full term at the Affiliated Drum Tower Hospital of Nanjing University Medical School from October 2006 to January 2007,were divided into two groups based on their mothers'status of anti-HBs(43 positive and 29 negative).All infants were vaccinated with hepatitis B vaccine at birth and one month thereafter.Serum anti-HBs were quantitatively determined for the mothers before delivery and for infants in cord blood at delivery and in serum at the age of 1 and 3.5 months. Results Anti-HBs of all 43 newborns in the positive group were positive in cord blood with the coefficiency of 0.98 to the maternal serum anti-HBs level(t=39.05,P<0.01).Forty-two out of the 43 infants remained anti-HBs positive at the age of 1 month.Anti-HBs was negative both at birth and 1 month old in infants of the negative group.However,all infants in both groups were anti-HBs positive at 3.5 months of age,while the average concentration of anti-HBs in infants of the negative group was significantly higher than that of the positive group [(466.9±86.7)mIU/ml vs(151.2±23.1)mIU/ml,t=2.72,P=0.011].Among the 5 infants whose maternal anti-HBs level>1000 mIU/ml,3 did not produce active antibodies against two doses of hepatitis B vaccination. Conclusions Passively acquired maternal anti-HBs in infants can inhibit the active antibody response to hepatitis B vaccine,and the extent of this effect is associated with maternal anti-HBs level.