Introduction: Argininosuccinic aciduria (ASA, OMIM #207900) is the second most common urea cycle disorder (UCD) worldwide, caused by deficiency of argininosuccinate lyase (ASL) and biochemically characterized by elevation of argininosuccinic acid and deficiency of arginine. In addition to hyperammonemia, hepatic fibrosis, hypertension, neurocognitive deficiencies, and trichorrhexis nodosa are the typical features of ASA. In this study, we reviewed the phenotypic, genotypic characteristics and treatment of all ASA patients in Korea and demonstrated the incidence of ASA in Korea is low. Methods: A total of five patients have been confirmed as ASA in Asan Medical center children’s hospital, Seoul, Korea since 1999. Their clinical findings, biochemical profiles and genotypic characteristics were retrospectively reviewed. Results: A total number of eighty patients were diagnosed as affected by UCD, and among them, only five patients (6.3%) had ASA. Two patients were diagnosed due to hyperammonemic encephalopathy in their neonatal periods. The other three patients were detected in their pre-symptomatic periods by newborn screening. Urinary argininosuccinic acid levels were significantly elevated in all patients. The recessive mutations of the ASL gene were identified in all the patients. Until the first decade of life, three patients had neurologic deficit with delayed development, two patients had hepatomegaly with unremarkable liver function tests, two patients had sparse and brittle hair, one patient showed transient hypokalemia, and all patients were normotensive. Treatment included protein restriction and oral supplementation of 100-150mg/kg/day L-arginine with nitrogen scavenging treatment. Conclusion: The current study indicates relatively very low prevalence of ASL deficiency in the Korean population. Unlike other UCD patients, chronic hepatic and renal dysfunction should be monitored on a regular basis.