Nine patients with biliary atresia (BA) were investigated from the aspect of biliary bilirubin conjugates. They were classified arbitrarily into the good prognostic group in which jaundice disappeared (serum total bilirubin equal or below 1.0 mg/dl), and the poor prognostic group in which persistent jaundice was observed for more than 12 months. The ratio of biliary bilirubin diconjugate (BDC) increased in all patients of the two groups by the first month after operation. Although there was no significant difference in daily bilirubin excretion within 1-3 postoperative days, the BDC ratio in the good prognostic group was significantly higher than that in the poor prognostic group (p < 0.01). The study indicated that the ratio of BDC was an early prognostic determinant of BA patients. The prognosis of BA patients was much influenced by the ability of bilirubin conjugation in the early postoperative days.