A total number of 143 infants at the age of 4 to 7 months from Yantai city-Shandong was selected for the study of antibody level against measles by maternal-fetal transfer and immuno-response to measles vaccine in October of 1993. The results showed that the negative rates of maternal-fetal antibody among infants of 4, 5, 6 and 7 month olds were 75.00%, 81.25%, 94.87% and 90.1%, respectively. The positive rates and geometric mean titers (GMTs) for immuno-response to measles vaccine were 92.86%, 84.38%, 97.44%, 100.00% and 55.17, 42.41, 69.95, 71.46, respectively. There were significant lower immune response to measles vaccine in infants who had high titer (> 1:2) than those who had low titer (<or= 1:2) of maternal-fetal antibody (chi 2 = 88.38, P < 0.001). In order to decrease the number of measles cases under 1 year old (especially under 9 month-old), the author suggested that the primary immunization for measles vaccine should be started at 6 month olds.