A 42-year-old man with hepatitis C virus infection, cryoglobulinemia, hypocomplementemia, and nephrotic syndrome is reported. The kidney biopsy showed membranoproliferative glomerulonephritis. The patient was treated with interferon-alpha for 2 months. After the treatment, serum hepatitis C virus RNA became negative and nephrotic syndrome remitted. Repeat biopsy of the kidney revealed an improvement in renal histology. This case confirms an association between hepatitis C virus infection and membranoproliferative glomerulonephritis and the usefulness of interferon-alpha for treatment.