Somatostatin secreting cells ( named D cells also) in whole digestive tract of mud eel were showed with ABC immunohistochemical method in cured gut paraff in section. The somatostatin secreting cells were only presented in gastric body, scattered mainly in gastric gland and a few were showed in mucous epithelium. According to cytoplasmic process of their bottom , four endocrine cell types could be distinguished in digestive tract and they all were presented in stomach of mud eel, but the number of type ó was the largest , types . and . were next, type ò was the smallest. D cells producing somatostatin had the most functions and the most complex types among endocrine cells in digestive tract, so stomach of mud eel was also an important endocrine organ. Epithelial cell of gastric gland observed with electron microscopy contained lots of tubuloresicular systems and some zymogen granules, which showed it could secrete acid and produce zymogen, so it belonged to oxynticopeptic cell. Apical membrane of intestinal epithelial cell contained lots of microrillis. Microrillis of juvenile mud eel were longer, denser and t idier that those of adult mud eel, which showed absorbability of juvenile mud eel was stronger than absorbability of adult mud eel.