Varying circumstances call for various types of donor hepatectomy. We report here on an unusual type of donor hepatectomy, right posterior segmentectomy. A 46-year-old sister of the recipient was the donor. Her preoperative CT showed that the right anterior portal vein originated from the umbilical portion of the left portal vein. Intraoperative cholangiography revealed that the right posterior hepatic duct joined the common hepatic duct in the extrahepatic area. Right posterior segmentectomy was performed without transfusion in the donor. The postoperative course proceeded favorably in both donor and recipient until postoperative day 41, when the recipient unexpectedly expired as a result of cerebral hemorrhage. The donor was discharged with good liver function. We can conclude that the right posterior segment of the donor can be used as a graft, when the volume of left liver is not enough for both donor and recipient, or the vascular structures favor right posterior segmentectomy.