Although the round ligament, including the umbilical vein, could be used as a venous graft in living donor liver transplantation (LDLT), no studies have determined its appropriate use on the basis of pathological findings. We prospectively examined 19 LDLT cases in which the donor's round ligament was procured and used as a venous graft. The round ligaments were categorized into 3 types based on the CD31 immunohistochemistry of tissue cross-sections: (I) canalized umbilical veins (n = 7 or 36.8%), (II) capillary umbilical vessels (n = 4 or 21.1%), and (III) occluded umbilical veins (n = 8 or 42.1%). After dilatation and incision, the round ligaments provided patch grafts that were 5.8 ± 0.4 cm long and 1.8 ± 1.2 cm wide. However, histological studies showed the absence of fine intimal layers on the dilated round ligaments after mechanical maneuvers. The ligaments were used to cuff the venous orifices in 15 patients (left lobe, n = 8; right lobe, n = 7) and were used as venous bridges in 4 patients (left lobe, n = 2; right lobe, n = 2). We detected no thrombosis at the implant sites after LDLT. Our pathological findings indicate that opened round ligaments can be used safely as venous patch grafts in LDLT. Liver Transpl 19:1245–1251, 2013. © 2013 AASLD.