Hepatitis C virus (HCV) infection leads to chronic liver disease, but it has also been associated with extrahepatic manifestations. Membranoproliferative glomerulonephritis (MPGN) is the most common renal disease associated with HCV. Although renal disease related to HCV in adults has been well studied, it has not been well studied in children because it is rare. A recent study found that antiviral therapy was effective for adult patients with HCV-associated MPGN. We report a 9-year-old girl with HCV-associated MPGN. Her HCV genotype was 1b, and her virus load was high. The first renal biopsy showed mesangial proliferation and partial double contours of the basement membrane on light microscopy and immunofluorescence staining with immunoglobulin (Ig) M, IgG, and C3. The patient was successfully treated with pegylated interferon (IFN) alpha-2a monotherapy. The antiviral therapy was generally well tolerated. After antiviral therapy, a sustained virological response-defined as negative HCV ribonucleic acid (RNA) at least 24 weeks after antiviral treatment-was achieved, the proteinuria disappeared, and the second renal biopsy showed improvement.