Abstract: The patients with colorectal melanosis often complain of vague abdominal pain, distention, decreased appetite and difficult defecation. In the examination, melanin deposited on the colorectal wall and a large quantity of macrophages containing pigment granules would be seen by light microscope. These marcrophages were remarkably increased in number and size. Much lipofuscin were found in cytoplasm by electron microscope. It is considered that colorectal melanosis is related to some factors such as difficult defecation, long time in take of high fat, high protein and low fibers, and the decreased colon motor function. These factors would influnce the interval of defecation and leave the time for melanotic substances in the faces to affect on the wall of the large intestine. Thus cause melanosis. This is also the etiology of the high incidence of cance and polyps among patients with colorectal melanosis. However the long time administration of laxatives and herbs like "R officinale baill" would also cause melanosis. Colorectal melanosis may be cured by operation on rectorele and internal intussusceptton. The patients had better take more exercise or have more fibrin is order to avoid administration of laxatives.