We investigated the antibody responses and clinical adverse reactions after immunization with live combined measles and rubella vaccine (HF vaccine) in 442 healthy children, aged 12-90 months of age. We obtained 368 paired sera. Among them, 363 were initially sero-negative against measles virus and 343 (94.5%) became sero-positive after immunization. Sero-conversion against rubella virus was demonstrated in 349 (96.7%) of 361 initially sero-negatives against rubella virus. We investigated the clinical adverse reactions in 406 recipients. In 102 (25.1%) recipients, febrile reaction (> 37.5 C) developed on the day 6.7 of vaccination on average, with a mean duration of 2.2 days. Only two (0.5%) developed high body temperature over 39.5 C. Skin rash was noted in 87 (21.4%) on day 7.1 of vaccination on average, with a mean duration of 4.8 days. Lymphoadenopathy was demonstrated in 12 (3.0%). Thus, measles and rubella combined vaccine was safe and sufficiently immunogenic as well as each monovalent one, having clinical advantage in immunization practice.