We followed students in eight elementary schools for rubella antibody from 1993 to 1996 (602 pairs) and 1996–9 (588 pairs) in Gyeonggi Province, Korea. We tested rubella IgG and administered rubella vaccine to the children with the titres <10 IU/ml. The loss rates of rubella IgG during the follow-up periods were 14·3 and 15·8%, respectively. Among vaccinated groups, the loss rate was 18·8%, which was significantly higher than 13·8% of the mixture of natural and vaccine-induced immunity groups. The group that had the lower preceding antibody titre had a higher loss rate of 24·8% compared to 7·2% for the group whose titre was 40 IU/ml or above. In a multivariate analysis, age and gender were not related to antibody loss rate. Under this higher rubella antibody loss rate, in order to prevent congenital rubella syndrome, the immunization for women at childbearing age appears necessary until rubella can be eliminated or controlled.