In biliary atresia, one-fourth of the patients showed prolonged jaundice in spite of a good excretion of bile after surgery. To investigate the cause of jaundice, factors related to the serum bilirubin level were examined in 28 recent cases. Furthermore, clinical analysis was performed in 86 cases of good excretion of bile after surgery. The following results were obtained: The daily amount of bilirubin excretion in bile and bilirubin concentration play an important role in decreasing the serum bilirubin level. The most important factor for prolonged jaundice is ascending cholangitis. Shortening of the life span of the red blood cells is one of the causes of prolonged jaundice.