Thirty patients with amyloidosis of the small intestine were studied to determine the correlations between the chemical types of amyloid protein and endoscopic, histologic, or clinical features. Endoscopic examinations of the jejunum revealed various findings such as a fine granular appearance, erosions and mucosal friability, thickening of the valvulae conniventes, and multiple polypoid protrusions in 23 cases. Immunohistochemical study of the biopsy specimens identified the following chemical types of amyloid protein: amyloid A protein (AA) in 20 cases, light chain protein (AL) in 8, beta 2-microglobulin (AH) in 1, and prealbumin (AF) in 1. The fine granular appearance was found significantly more often in the AA cases (p < 0.001), whereas multiple polypoid protrusions and thickening of the valvular conniventes were observed only in the AL cases (p < 0.001). Histologically, wide granular amyloid deposits in the propria mucosae were seen significantly more often in the AA cases (p < 0.01), whereas massive amyloid deposits in the muscularis mucosae, submucosa, and muscularis propria were the more dominant findings in the AL cases (p < 0.001). Clinically, a more frequent occurrence of diarrhea, malabsorption, and occult blood in stools was present in the AA cases, whereas mechanical obstruction and chronic intestinal pseudo-obstruction were evident only in the AL and the AH cases. These results suggest that clinicopathologic differences between the amyloid proteins exist in small intestinal amyloidosis and that endoscopic appearance relates to the specific accumulation pattern of each type of amyloid protein.