Abstract: The pancreas of Mastacembelus aculeatus is a distinct and compact organ, situated definitely in an area between the ascending and descending parts of the duodenum,irregularly extending along the hepatic portal vein and the mesenteric artery and their branches.Embedded in the pancreatic tissue,there are a number of large islets which can be readily recognized macroscopically and of which one dorsal and one ventral are the largest and constant in occurrence.The measurements and the frequency of occurrence of these isets are recorded in the table 1 and the table 2. The largest islets of Mastacembelus is enveloped in a membranous capsule and always associated with pancreatic exocrine tissue.Fine granules of the islet cell take acid fuchsin only if Mallory stain has been used,so that the islet cell may be of the same nature as the a—cell of the islet of Langerhans in the human material.In the exocrine portion of the pancreas,the acini are readily seen.Elongate cuboidal cells arranged in the form of a tube appear to be the transitional form of cells in the transformation from tubules to acini. Another kind of elongate cell is of undetermined nature.