Crigler-Najjar syndrome is a rare inherited disease associated with unconjugated hyperbilirubinemia. It is inherited via an autosomal recessive pattern and is caused by mutation in one of the five exons of the bilirubin uridine-diphosphoglucuronate glucuronosyltransferase (UGT1A1) gene. The synthesis of inactive isoforms of bilirubin uridine-diphosphoglucuronate glucuronosyltransferase (B-UGT) results in unconjugated hyperbilirubinemia. A 13-year-old boy with jaundice for 4 months was admitted to our hospital. He had unconjugated hyperbilirubinemia with no evidence of infection, hemolysis, or structural abnormalities on abdominal ultrasonography or 99mTc-DISIDA scan. The authors identified a missense mutation of Tyr486Asp in the fifth exon of the UGT1A1 gene and diagnosed the patient with Crigler-Najjar syndrome type II. This is the first reported case of Crigler-Najjar syndrome in a Korean child, and it is also the first reported case of a genetic mutation leading to Crigler-Najjar syndrome in Korea.