A 47-year-old man with primary amyloidosis confined to the small intestine is reported. Thickening of the folds and multiple polypoid protrusions were found in the duodenum by upper gastrointestinal endoscopy. Because the patient presented with a persistent intestinal pseudo-obstruction, partial jejunectomy was performed. Histological examination of the resected tissue revealed massive deposits of amyloid throughout the jejunal wall. Neither a predisposing condition nor any other sites of deposition were found, and primary amyloidosis of the small intestine was diagnosed. This rare form of amyloid deposition should be recognized so that an early diagnosis can be made.