We experienced a 24-year-old Japanese man, who was a hepatitis B virus carrier with nephrotic syndrome. Liver biopsy showed that he was suffering from chronic hepatitis (activity 2, fibrosis 2). Renal biopsy revealed membranous nephropathy(MN) with focal segmental glomerulosclerosis(FGS). Immunofluorescentic findings revealed the presence of HBe antigen along the glomerular capillaries as well as HBe antigenemia in circulation. Therefore, we diagnosed this case as HB virus-related membranous nephropathy associated with FGS lesions. He was treated with interferon(IFN) alpha-2b for over a month and angiotensin converting enzyme inhibitor. These therapies reduced urinary protein excretion from 4-6 g/day to 1-2 g/day, in accordance with a decrease in the titer of HBV DNA polymerase. The second renal biopsy revealed that the histological change from MN to membranoproliferative glomerulonephritis Type III after IFN therapy. These results suggest that IFN therapy might be effective for HB virus-related MN associated with FGS.