Leptospirosis is a worldwide zoonosis and common in tropical and subtropical areas with high rainfall. It should be noted as an imported infectious disease although it is sporadic in Japan. Some imported cases already have been reported in Japan and these cases occurred mainly in Southeast Asia. The case discussed in this article is the first reported Japanese case infected in Vietnam. Four days after returning back to Japan after a two-week stay in the mountain area near Hue, in the middle part of Vietnam, the patient suddenly experienced chills, a high fever, sore throat, gastrocnemius pain, and headache. Conjunctival jaundice, renal function disorder, and proteinuria were observed on the third day of onset. Significant increase in antibody titers against serovar Australis and Autumnalis strains was observed in paired serum samples by microscopic agglutination test (MAT). Consequently we recognized this case as a diagnosis of severe leptospirosis (Weil’s disease). Finally, renal function disorder did not deteriorate further, and then the patient recovered after the tenth day of onset with the administration of antibiotics and supportive care without sequelae. We experienced the first imported Japanese case of severe human leptospirosis infection from Vietnam that was successfully treated with ceftriaxone and minocycline.