The study of liver function and diseases requires detailed knowledge of the regional anatomy of and surgical approach to the vascular supply of the liver. The objective of this study was to systematically describe the regional anatomy of the circulation to the rat liver to facilitate the planning and performance of future studies of the liver in this animal. Twelve adult rats underwent general anesthesia and vivisection of the celiac axis and portal vein using an operating microscope. The major vessels of these vascular systems were evaluated for their origin, course, relationship with neighboring structures, diameter, and length. All vessels were easily visualized by a ventral approach after mobilization of the intermediate lobe of the liver and its papillary process. The origin and course of the major vessels are similar to those of humans, and variability in vessel origin was identified in this small number of animals. Median vessel diameters were between 0.5 and 1 mm (range, 0.25 to 1 mm) for the celiac artery and its branches, and 3 mm for the portal vein (range, 2 to 3 mm). Median vessel length was between 3 and 7 mm (range, 2 to 8 mm) for the celiac artery and its branches, and 7 mm for the portal vein (range, 4 to 8 mm). The anatomic description obtained in this study is important for the appropriate selection of vessels for cannulation or ligation during study design, as well as vessel isolation during performance of the study. The diameter and length of vessels are important in the selection of appropriately sized catheters and perivascular devices.