Abstract: To observe immunologic memory for HBsAg among vaccinees with vaccine induced anti HBs negative-conversion 9～10 years after infancy plasma derived hepatitis B vaccine immunization.Methods RIA was used to exame and compare the anti HBs levels of subjects between hepatitis B vaccine pre and post booster.Results Anti HBs positive rate and titer of 48 subjects after booster were significantly higher than that before booster(P<0.01);70 9%(34/48) of subjects kept immunologic memory which had at least persisted 3 years.Conclusion Majority of children who were vaccine induce anti HBs negative conversion vaccinated had kept immunologic memory and no evidence for need to booster,9～10 years after three doses of hepatitis B vaccine immunization in infancy.