This work was carried out on some plectognathid fishes to study the normal histological structure of the liver. They contained puffer fishes, Arothron hispidus and A. stellatus; porcupine fish, Diodon hystrix; and blue trigger fish, Pseudobalistes fuscus. Specimens of these fish species were collected from the Red Sea.Histological results showed that the liver was composed of hepatic parenchyma which externally covered by a loose connective tissue and a layer of squamous epithelium. Hepatocytes are radially arranged around a central vein in interconnecting laminae of two cells thickness, separated by blood sinusoids. They are big and rounded or oval in shape with transparent cytoplasm, because of the presence of a large quantity of lipids. It contained a large, rounded, and peripherally nucleus with a prominent dark nucleolus.The pancreatic tissue is distributed in the liver as hepatopancreas. Thin septa of connective tissue separated pancreatic cells from hepatocytes. The pancreatic cells are tall and columnar, with spherical and basal nuclei, having prominent dark nucleoli. Zymogen granules are located in the apical ends of these cells. The results showed the presence of melano-macrophage aggregations in hepatic parenchyma of all studied fish species of tetraodontiformes.