Few reports have described the influence of the retroportal artery on the distribution of anticancer drugs in the liver during repeated hepatic arterial infusion chemotherapy. This report describes two patients in whom poor distribution was observed in the right lobe of the liver, which was confirmed at superior mesenteric arteriography to be caused by inflow of the retroportal artery to the right hepatic artery. The retroportal artery was successfully embolized, resulting in improvement of distribution in the right lobe of the liver in both cases.