The normal structure of the liver of Gilthead sea bream, an economically valuable marine fish, was studied using LM and electron microscopy.The liver was covered by a thin fibrous connective tissue capsule, and a single layer of mesothelial cells. The parenchyma of the liver was not divided into lobules. The biliary channels and vascular elements seemed to be randomly dispersed throughout the parenchyma. The liver was formed of a mass of cells penetrated by sinusoids. Within the parenchyma, the hepatocytes spread out as irregular cords arranged in two cellular layers surrounded by sinusoids. Hepatic sinusoids were lined by endothelial cells with elongated dark nuclei. The endothelium separates the space of Disse incompletely from the lumen of sinusoids.The hepatocytes were hexagonal in shape, had spherical pale- stained and centrally located nuclei that showed one or more nucleoli. Binucleated cells were sometimes visible. ultrastructurally hepatocytes showed large, spherical and rounded nuclei. The nucleus contained one or more prominent nucleoli. It was pale euchromatic and showed some heterochromatin at the periphery. The microvillus surface of the hepatic cells was clear in the space of Disse, interhepatocytic surface and canalicular surface facing the bile canaliculi. The cytoplasm had abundant amounts of R.E.R while S.E.R. was few. Numerous mitochondria, large amount of glycogen as well as many lipid droplets were also seen. Different cells rather than hepatocytes were observed in the parenchyma. Melanomacrophage centers appeared as group of macrophage with chromolipoid material and melanin pigments. A second type of non hepatocytic cell was located in the   perisinusoidal space and called "perisinusoidal cell". A third non hepatocytic cell type was found wedged in between adjacent hepatocytes at the sinusoidal side. Between hepatocytes in a midst position there was another type of cells with elongated nuclei and dispersed chromatin, with cytoplasmic processes extending between hepatocytes.  The intraparenchymal macrophage cells were located among the hepatocytes.