In a Muscovy duck breeding-growing farm in Aomori prefecture, most of ducklings hatched during spring in 1994 died within two-week-old. The mortality was nearly 100%. In most cases, birds died without clinical signs and some with leg weakness. By serological and virological tests, the outbreak was identified as a goose parvovirus infection. In pathological test, however, no typical manifestations of goose parvovirus infections (hepatitis and intranuclear inclusion bodies in hepatic cells) were detected.