Portal vein thrombosis (PVT) is a rare complication that occurs after liver transplantation: however, it cannot be ignored as a cause of graft loss and death. We herein report a pediatric case of PVT that caused a fatty change in the graft after living donor liver transplantation. The portal vein was successfully reconstructed using the left great saphenous vein of the same donor. Moreover, the fatty liver recovered after the operation. Our case suggests that the finding of fatty liver is an important marker of PVT and immediate portal reconstruction is performed.