We report a rare autopsy case of secondary gastrointestinal amyloid A (AA) amyloidosis associated with idiopathic retroperitoneal fibrosis (IRF) in a 67-year-old woman. Masses were identified around the aorta and inferior vena cava in her abdomen. Histologically, plasma cell infiltration was observed within fibrotic areas. Because no specific cause for the inflammatory mass was apparent, we diagnosed it as IRF. Steroid therapy, which usually reduces IRF masses, proved ineffective, and malabsorption syndrome developed 4 years later. On autopsy, amyloid protein was present systemically in the vascular walls of several organs, and deposition was highest in the gastrointestinal mucosa. Amyloid protein was identified as AA type, strongly suggesting that the amyloidosis was secondarily induced by IRF. To our knowledge, only 2 other cases of IRF-associated amyloidosis have been reported. Two of the 3 patients of these cases were women who showed resistance to steroid therapy.