Cholinesterase (ChE) is an enzyme synthesized in the liver. The aim of this study was to determine the value of ChE as an index of liver function. We measured the ChE activity as well as the values of bilirubin, alkaline phosphatase, gamma-glutamyl transpeptidase, aminotransferases and albumin before and 7 days after Kasai operation in 25 infants with biliary atresia. The increased activity of ChE in plasma after Kasai operation was accompanied by a decrease of other measured values ( P<0.0001), except for albumin. We can conclude that the increase of ChE activity together with the decrease of bilirubin, alkaline phosphatase and gamma-glutamyl transpeptidase show early improvement of liver function after Kasai operation. ChE activity can be used to assess liver function in terms of synthesis.