This study compared the seasonal changes in the activities of primary school children in Hirosaki (a northern snowy city in Japan) with those in Hiroshima (a western warm city) for the six consecutive months starting October, 1988. The activity level was defined in terms of the frequencies per hour counted by an actigram. The following results were obtained: (1) Boys are more active than girls; (2) Both the girls in Hirosaki and in Hiroshima did not show any seasonal changes in their activity levels; (3) Only the boys in Hiroshima decreased their activity level during winter, while the boys in Hirosaki maintained their level; (4) For the boys in Hiroshima, their activity level was correlated positively with low temparature and negatively with the amount of rainfall.