Seasonal distribution of diarrheal viruses including rotavirus and norovirus was studied among children with acute gastroenteritis in Japan (5 areas), China (Kunming), Vietnam (Ho Chi Minh) and Russia (Birobidzhan) between 2000 and 2004. The relation between time (month), climate and serotype/genotype of the detected viruses were investigated. The collected samples and relevant periods were not same among countries. Rotavirus infection was detected all year-round in the country where the climate does not change in seasons, such as Vietnam, however, it was also found in wintertime where four seasons exist. Rotavirus was identified in late winter and norovirus in early winter in Japan. G1 rotavirus was predominant in 199th, however its number has decreased from 200th in Japan from our previous reports and this report. GII/4 norovirus was the most prevalent in the examined period, followed by GII/3. Climate, year and area, and probably also immunological factor in children are related to the distribution of the diarrheal viruses.