Measles outbreak in the world was decreased since measles vaccine had been introduced. Although vaccination rate is high, measles was not eradicated and measles reappeared among vaccinated children. We measured measles-specific antibody from the vaccinated and unvaccinated groups who had experienced apparent measles in the Seongnam city in 1993. The results were as follows. 1) The data included total 126 children (M:F=1 : 1). Age distribution of measles outbreak revealed 6 children in 5yr, 11 in 6yr, 20 in 7yr, 39 in 8yr, 22 in 9yr, 11 in 10yr, 11 in 11yr, and 6 in 12yr. 2) MMR vaccination rate was 78.6%(99/126) in the children who had experienced measles. Positive rate of measles-specific IgM Ab was 80.8% (80/99) among the vaccinated group and among 9E.6.% (25/27) the unvaccinated. 3) Positive rate of measles-specific IgG Ab was 90.9% (90/99) among MMR-vaccinated group, and 85.2% (23/27) in unvaccinated group. In conclusion, measles-specific IgM antibody have been detected more than 1 month in most patients. The relatively high proportion of measles-specific IgM positivity may mean primary vaccine failure. To booster the antibody titers and to prevent measles epidemic in school-aged children, revaccination of measles should be considered.