Abstract: A 57yearold man was admitted to the hospital with hypertension and renal hypofunction for 2 years. During the course of the disease,he lost 5 kg of body weight,splenomegaly and increased peripheral blood lymphocytes.Bone marrow flow cytometry showed that lymphocytes accounted for 365% of nuclear cells,of which B cells accounted for 78%,expressing HLADR,CD5,CD19,CD20,CD22,sKappa (dim) and negative for lammda. Renal biopsy revealed glomerular proliferative lesions with single IgG3 deposition and multifocal interstitial infiltration of CD20 positive cells. The final diagnosis was membranous proliferative glomerulonephritis with monoclonal IgG3 deposition and Bcell chronic lymphoproliferative disease.After treatment with Rituximab for 13 months,serum creatinine and urinary protein decreased. This is the first case of membranoproliferative nephritis caused by B lymphocyte proliferative disease reported in China. For proliferative glomerulonephritis with persistent lymphocytosis of unknown etiology,B cell chronic lymphoproliferative disease should be excluded.