Different anatomical variations of the intrahepatic bile ducts, and in particular its right half, is one of the important risk factors for billiary complication in recipients undergoing living-donor liver transplantation (LDLT). The authors already reported high risk group of biliary injury during living donor hepatecotmy according to the anatomy of the right posterior bile duct (RPBD). We experienced a case with the bile duct injury in the graft which was unnoticed during living donor hepatectomy. 26 years old male underwent right liver hepatectomy for donation to his father 55 years old. The preoperative MRCP showed long caudal segment of RPBD, which has been reported as high risk for biliary complication in the recipient. There was no problem during donor hepatectomy and bench surgery. However, we found that RPBD was not easily identified and RPBD was partially ligated when probing was tried just before biliary anastomosis. We opened ligated RPBD. But the wall was thin. We opened damaged wall of RPBD and duct-to-duct anastomosis was done without stent. According to this case, we learned several lessons: 1) Understanding of the preoperative risk of bile duct injury during hepatectomy based on preoperative MRCP is important, 2) different bile duct division method in the high risk patient should be applied, 3) comparison of the biliary anatomy by probing the graft during bench with that of preoperative MRCP is necessary to detect unknown bile duct injury, 4) injured wall should be opened and anastomosed using healthy duct is important to reduce delayed biliary complications.