In order to evaluate the changes in Japanese Cedar (JC) sensitization rates of allergic children, serum samples from 88 patients about 15 years ago (past group) and those from 91 current patients (present group) were randomly selected, and their JC specific IgE were measured with the CAP-RAST system. Sensitivity rate (class 2 or more) for JC of the present group was 65.9%, which was significantly higher than that of the past group, which was 46.6%. However, there was no significant difference between these two groups for children aged 6 or younger. For children aged 7 or older, the sensitivity rate of the present group was significantly higher than that of the past group. Thus, protection against JC sensitization, especially during early childhood, should be given serious attention.