Trivalent vaccine, containing measles TD97, rubella TCRB-19 and mumps NK-M46 strains (MMR vaccine) was administered to a total of 116 healthy children of which 50 subjects were simultaneously injected with varicella vaccine in the opposite arm. The seroconversion rates for measles, mumps, rubella, and varicella in those who received both MMR and varicella vaccines (MMR + V group) were 100%(44/44), 91%(39/43), 100%(46/46) and 95%(39/41), respectively. And these rates were comparable to those in subjects receiving only MMR vaccine, namely 100%(64/64) for measles, 95%(57/62) for mumps, and 97%(58/60) for rubella. Fifty-eight children receiving MMR vaccine were seronegative to measles, mumps and rubella before vaccination, and 51 (88%) of them were found to be seropositive against all three viruses at 6 to 8 weeks after vaccination. Among the children injected with MMR and varicella vaccines, 36 subjects had no pre-antibodies to measles, mumps, rubella and varicella. Seroconversion in post-serum to all four viruses were found in 31 cases (86%). Clinical reactions observed in some vaccines were mild fever (17%) and exanthem (5%). There were no complications of lymphadenopathy, swelling in parotis regions, or meningitis. Our results indicate that simultaneous administration of MMR vaccine and varicella vaccine is a safe and effective method for immunizing children against these four infectious diseases.