Although there have been many studies of the corneal endothelium of human and some mammals, there have been few in other vertebrates. The purpose of this study was to examine the posterior endothelial surface and to perform a morphological analysis of the corneal endothelial cells of normal Wistar rats. Twenty-four normal eyes from twelve Wistar rats (Rattus norvegicus) were studied. These animals were obtained from the biotrepy of the Faculty of Biochemistry of the Federal University of Rio Grande do Sul. All studies were approved by the institutional Animal Care and Use Committee and were performed in compliance with the ARVO statement for use of animals in ophthalmic and vision research. Ophthalmic examination was performed before enucleation. Eyes with evidence of ocular disease were excluded. The subjects were divided in four groups with three rats in function of age: G1 (30 days old), G2 (45 days old), G3 (90 days old), G4 (150 days old). Immediately after death the both eyes were removed and the endothelium stained alizarin red and examined using a light microscope. Three photomicrographs were taken of each cornea. The images were made with magnification the x10, x20 and x40. The analysis was performed with regard to polygonality. Normal Wistar rat corneal endothelium was characterized by a continuous layer of polygonal cells of uniform size and shape. The predominant number of cells all groups was hexagonal. The parameters evaluated did not differ significantly between groups analyzed from the rats. The results staining with the alizarin red provides a simple, quick technique for visualization of corneal endothelium. In conclusion, the results revealed that the pleomorphism showed constant valued on the four groups increase as function of age.