Adult-onset type II citrullinemia (CTLN2) is a disorder caused by an inborn error of metabolism affecting the liver. CTLN2 is an autosomal recessive disorder characterized by recurrent encephalopathy with hyperammonemia due to highly elevated plasma levels of citrulline and ammonia, caused by a deficiency of argininosuccinate synthetase in the liver. A small number of patients have undergone liver transplantation with favorable results. In Korea, the limitations of the deceased donor pool have made living donor liver transplantation a common alternative treatment option. We report the case of a patient with type II citrullinemia who was treated successfully with auxiliary partial orthotopic liver transplantation (APOLT) from a living donor. This is the first description of an APOLT for a patient with adult onset type II citrullinemia in Korea.