Epstein–Barr virus (EBV) is the causative agent of infectious mononucleosis and some malignancies including EBV-associated-lymphomas. A large portion of adults all over the world are infected with EBV. In children, however, there are geographic variations. Most of the children in Asia and in other developing countries are infected in their early life, before 1 year of age (>90% of 5–9-year-old children are infected), while the age of primary infection is delayed in Western countries (approx. 50% of 5–9-year-old children are infected). The purpose of the present paper was to investigate the recent time trend of the EBV seropositivity among 5–7-year-old children living in Tokyo and its neighboring prefectures. Indirect immunofluorescein study for IgG antibody to viral capsid antigen was performed on 442 archival sera. Before the early 1990s, >80% of 5–7-year-old children were found to be seropositive, while the positivity rate decreased to 59% (P < 0.001) for the years 1995–1999. These results also showed that the delay in the age of primary infection is continuing and that the rate is estimated to be <50% in 2006. This result suggests that the delay will affect the incidence of EBV-associated disorders in Japan.