Abstract: Using immunohistochemical staining technique of the peroxidase-anti-peroxidase (PAP), 10 kinds of antisera raised against mammalian hormones were investigated with regard to the identification and distribution of endocrine cells in the intestinal mucosa of common carp(Cyprinus carpio) and black carp (Mylopharyngodon piceus). Endocrine cells in the intestinal mucosa of common carp reacting with antisera against 7 different mammalian polypeptide hormones were localized, and 6 kinds of antisera were localized in black carp. Positive reactions were obtained with antisera againt gastrin(GAS), substance P(SP), bovine pancreatic polypeptide(BPP), leucine enkephalin(ENK), glucag on-like immunoreactants(GLI), gastric inhibitery peptide (GIP), and somatostatine(SOM). No immunoreactivities were found with antisera against meurotensin(NT), 5-hydroxytryptamine(5-HT) and cholecystokinin(CCK) in the gut of common carp and black carp, or with antisera against somatostatine(SOM) in the gut of black carp. Most kinds of the immunoreactive endocrine cells had the highest distribution density in the anterior segment of the foregut of common carp and black carp. But in the gut of black carp, SP and ENK endocrine cells had the highest distribution density in the rectum, while GLI endocrine cells had the highest distribution density in the midgut. In common carp, BPP and ENK endocrine cells had the highest distribution density in the posterior segment of foregut, SP and GLI endocrine cells had the highest distribution density in the midgut, and none of the immunoreactive endocrine cells was found in the rectum. GAS and SP endocrine cells were mostly located in the top of the gut folds; the rest were mostly located in the basal and middle parts of the gut folds. Almost all kinds of immunoreactive endocrine cells were of the open type. In some endocrine cells, the basilar cytoplasmic process extended to the basement membrane and adjacent cells, and formed synapse-like contact with basement membrane. This phenomenon provided morphological evidence for neuroendocrine and paracrine secretion of enteroendocrine cells. It is noteworthy that SP, ENK and SOM are neural peptides, their immunoreactive endocrine cells were found in the intestinal mucosa of fishes. This phenomenon providesnew evidence for the concept of brain-gut peptides. In the present paper, the morphological, characteristics of immunoreactive endocrine cells were described. Their distribution density in all intestinal segments of common carp and black were compared. Their distribution characteristics, the possible way of secretion and function were discussed.