Malignant neoplasms are rarely associated with glomerular changes. The glomerular lesion seen most often in patients with malignancies is membranous glomerulonephritis. We report here a case of gastric cancer associated with rapidly progressive glomerulonephritis (RPGN). A 57-year-old man was admitted to our hospital with acute renal failure. Renal biopsy was performed, and the diagnosis was RPGN. Steroid treatment was instituted, but was complicated by hematemesis, and an early-stage gastric cancer was found after endoscopic examinations. Gastric biopsy revealed gastric adenocarcinoma. The patient's renal function improved with corticosteroid treatment and hemodialysis, and total gastrectomy was performed. The improvement in renal function persisted after the removal of the gastric cancer, and the RPGN and cancer have been in remission for 3 years.