Aim: MMR vaccine is a part of the NIP and is widely used in children throughout Korea. However studies on the currently used vaccines in Korean children are scarce. In this study, we evaluated the immunogenicity and safety of two MMR vaccines in Korean children. Methods: For primary and second dose immunization, children aged 12-23 months and 4-6 years were enrolled. All subjects received a single dose of either Priorix™ or MMRII®. Pre- and postvaccine sera were collected from all participants. Antibody levels were determined by ELISA kits (Enzygnost®; Dade Behring, Schwalbach, Germany). For the evaluation of mumps PateliaTM Mumps IgG (BioRad, Marnes-la-Coquette, France) was also done. Parents or guardians were issued with a diary card to record solicited local adverse events for 5 days and any systemic adverse events for 42 days following vaccination. Results: A total of 160 Korean children were enrolled. For the primary dose, 121 subjects were enrolled in the 12-23 months age group. For the second dose, 39 were enrolled in the 4-6 years age group. Among the prevaccine sera, 0.9% of the 12-23 months age group had anti-measles and anti-rubella IgG and none of the children had anti-mumps IgG. Among children 4-6 years, 96.3%, 88.9% and 96.3% of the children had antibodies for measles, mumps and rubella before vaccination. The seroconversion rate for previously seronegative subjects of 12-23 months age group was 100.0% for measles, 93.2-96.2% for mumps and 100.0% for rubella. There was no significant difference in geomean titers or seroconversion rates between the two study vaccines. In children 4-6 years of age who were previously seronegative, all children showed seroconversion for measles, mumps and rubella. For the safety analysis, 9.8-10.7% (12-23 months age) and 14.3-19.2% (4-6 years age) of the subjects experienced at least more than 1 local adverse reaction and 21.4-31.1% (12-23 months age) and 17.9-23.1% (4-6 years age) experienced at least more than 1 systemic adverse reaction. No vaccine-related serious adverse events were reported. Conclusion: The current MMR vaccines in Korea showed good immunogenic responses for measles, mumps and rubella in 12-23 months and 4-6 year old children. Both vaccines are safe and the results of this study could be used as important basic data when considering MMR immunization strategy in Korean children.