PURPOSE: In order to evaluate the time of disappearance of cytomegalovirus(CMV) IgG antibodies from mothers, and the alteration of the positive rate of CMV IgG antibodies among preschool period children, we investigated the positive rate of CMV antibodies among preschool children. METHODS: We studied 391 children who visited the Department of Pediatrics from March, 2001 to February, 2004. We measured the serum CMV IgG of 217 children and the serum CMV IgM of 358 children. RESULTS: The positive rate of CMV IgG antibodies is 83.9 percent(the number of positive IgG children is 182 out of 217). The alteration of the positive rate is 92.9 percent in 0-3 months, 75.0 percent in 4-6 months and the nadir was 20.0 percent in 7-9 months. Then, the positive rate increased to 83.9 percent in 22-24 months. After 22 months, the positive rate was 92.1 percent(the number of positive IgG children was 105 out of 114). The positive rate of CMV IgM antibody by age is 3.3 percent in 0-1 months, 3.6 percent in 1-2 months, 10.5 percent in 2-3 months, 14.3 percent in 3-4 months, 14.3 percent in 4-5 months, and then the results of five children among 148 children were positive. The distribution was one in 22-23 months, one in 25-26 months, one in 27-28 months, one in 28-29 months, one in 40-41 months. We discovered IgM positive children succesively from birth to 5 months, but sporadically after 5 months. CONCLUSION: The CMV IgG from mothers has decreased since birth and the time of nadir is 7-9 months. But it increases to a mean value of 83.9 percent at 22-24 months because of perinatal or postnatal infections.