A 51-year-old Japanese woman with Budd-Chiari syndrome, following dermatoplasty of the leg for burns, developed multiple myeloma and amyloidosis during the four-year observation period. In Budd-Chiari syndrome, polyclonal hypergammaglobulinemia is frequently seen as the result of intestinal antigenic stimulation through the portacaval shunt. Although monoclonal gammopathy is occasionally presented in chronic liver diseases, multiple myeloma has not been previously recognized as occurring in association with Budd-Chiari syndrome. This case demonstrates that, in Budd-Chiari syndrome, the development of multiple myeloma may be the result of chronic stimulation of the intestinal microbes.