AbstractTo elucidate the bile acid metabolism in the preoperative and postoperative stages of congenital biliary atresia (CBA), the unconjugated and conjugated bile acid levels in sera were measured by high performance liquid chromatography (HPLC). The results showed that the mean total serum bile acid (TSBA) level in the preoperative cases of CBA was higher, 122.1±39.0n̈mol/1 (1SD), and was about 12 times higher than the level in the age‐matched normal controls (9.9±6.0). Even in the non‐icteric patients several years after operation, the mean TSBA level was still much higher (15.2±9.6) than that of normal controls (5.7±3.1). The mean ratio of cholic acid to chenodeoxycholic acid (CA/CDCA) in the preoperative and postoperative cases of CBA was less than 1.0. The mean ratio of glycine‐conjugated bile acids to taurine‐conjugated bile acids (G/T) in the preoperative cases of CBA was the lowest (1.9±1.1). In the clinically good cases with sufficient bile flow after operation, G/T ratio was the highest (9.3±6.5). In the normal controls and the patients with preoperative and postoperative CBA, the main bile acids were glycocholic acid, taurocholic acid, glycochenodeoxycholic acid and taurochenodeoxycholic acid. These conjugated bile acids comprised more than 85% of the t