The liver is the largest gland in digestive system. The most parts of liver is placing in right region of abdominal cavity. It is fixing by special ligaments, arteries and veins. The blood of digestive system is drained into liver by caudal venacavae and then it is drained of liver by hepatic portal vein. In this survey, relationship between caudal venacavae with hepatic veins, type of hepatic veins and also manner of drainage of hepatic veins are studied. 16 healthy and mature dog are selected and theme's liver is studied. Results of liver biometry are followed: Average of weight = 0/794 kg Average length = 25/38cm Average wide = 16/4cm Average of thickness = 5/58cm Average length of gall bladder = 3/53cm Average diameter of portal vein in initial part = 5cm. Liver veins were short veins which are occupied parenchyma of liver. These veins are received more branch of small veins. All of these veins were draining into abdominolateral wall of inter hepatic part of caudal venacavae. Results of this research are shoved which inter hepatic veins have different diameter. Rang of these diameter was from 0.2 to 5mm. Based on diameter of interhepatic veins, they are arranged into 3 category. 1- large inter hepatic veins with diameter 5mm or more. 2-Intermediate interhepatic veins with diameter 1 to 5mm. 3- Small interhepatic vein with diameter less of 1mm. The studies on derivatives of hepatic veins in this research on the dog are appeared that portal veins received two-principle trunk (right trunk and left trunk). 6 veins branches were draining the blood of right aspect of liver into right trunk and 11 veins branches were draining the blood of left aspect of liver into left trunk. In totally 17 veins branches arose liver and blood of liver is drained by them.