Electropherotypes (ET), serotypes, and subgroups of equine rotaviruses isolated from foals in Japan were determined. The ETs of 136 isolates from 1981 through to 1991 were divided into six groups: ET-A-ET-F. The ET-A,-B,-C,-D,-E, and -F were present in 3, 1, 121, 9, 1, and 1 strains, respectively. Representative viruses of ET-A, -B, -C, and -D were identified as serotype G 3. Viruses of ET-E and -F were identified as serotypes G10 and G5, respectively. The four representative viruses of serotype G3 did not belong to either subgroup I or II. The two viruses of serotypes G5 and G10 belonged to subgroup I. Serotype G3 strains possessing ET-C were prevalent among the foals throughout the study period.