We report a case of nephrotic syndrome associated with MALT lymphoma. The patient was a 66-year-old woman who had a 21-year history of MALT lymphoma. She was admitted to our hospital for the evaluation of systemic edema and purpura during two months. Urinary protein excretion was quantified at 3.3 g/24h. Serum creatinine was elevated to 1.63 mg/dL. An immunoserological investigation showed the presence of IgM-kappa type monoclonal cryoglobulin accompanied by a decreased serum complement level. HCV infection was negative. A renal biopsy specimen revealed membranoproliferative glomerulonephritis (MPGN) with cryoglobulin deposition and focal atypical lymphoid cells infiltration in the renal interstitium. Immunoperoxidase staining of the atypical lymphoid cell population was positive for CD20 and CD79. Combined therapy with prednisolone, plasma exchange and rituximab was commenced. Her proteinuria disappeared and renal function improved after rituximab therapy. In our case, nephrotic syndrome due to cryoglobulinemic glomerulonephritis was successfully treated mainly by rituximab.