The sequential or simultaneous presentation of anti-glomerular basement membrane (anti-GBM) glomerulonephritis with membranous nephropathy (MN) has been infrequently reported. Although the mechanism underlying MN superimposed on anti-GBM glomerulonephritis is unknown, the two entities are believed to be interrelated. We report the case of a 75-year-old woman diagnosed with rapidly progressive glomerulonephritis. Renal biopsy revealed crescentic glomerulonephritis with linear and granular staining of immunofluorescent IgG1 and IgG4 granular staining on the capillary loops. Electron microscopy revealed extensive subepithelial deposits. These findings suggested simultaneous development of anti-GBM glomerulonephritis and MN in this case. Serum phospholipase A2 receptor (PLA2R) antibody was negative. The patient was treated with prednisolone and plasma exchange, resulting in resolution of renal insufficiency and a decrease in urinary protein. The rapid decrease in urinary protein and absence of PLA2R antibody suggest that the mechanism of MN associated with anti-GBM glomerulonephritis differs from that of primary MN.