A 79-year-old woman was admitted to our hospital presenting with bloody stool. Colonoscopic examination showed many irregularly-shaped discrete ulcerations in the sigmoid colon extending for a length of 6 cm, situated 16 cm proximal to the anal ring. Histopathology of the biopsy specimen in and around the ulcerations revealed the deposition of amyloid materials in the proper mucosa and the submucosa. Similar ulcerations were not detected by endoscopy in other parts of the gastrointestinal tract, i.e., esophagus, stomach, and duodenum. Multiple biopsy specimens taken from various parts of the gastrointestinal tract other than the sigmoid colon showed no amyloid deposition. Further investigations showed no particular abnormality in any organs and the patient was free of such systemic disease as myeloma or collagen disease. The findings were consistent with those of localized sigmoid amyloidosis. Localized colonic amyloidosis is rare, this being the fifth patient reported in Japan in the past 15 years.