Objective To evaluate the accuracy of bispectral index (BIS)-guided closed-loop target controlled infusion (TCI) system in comparison with opened-loop manual TCI during anesthesia of biliary tract and pancreas surgeries.Methods Forty adult patients undergoing open surgery of biliary tract or pancreas under total intravenous anesthesia, including 17 males and 23 females, aged 18-75 years, falling into ASA physical status Ⅱ or Ⅲ, were randomly allocated into closed-loop group (group C, n=20) and opened-loop manual group (group M, n=20).In group M, the propofol effect-site concentration was adapted at the discretion of the anesthesiologist to reach and maintain a BIS as close as possible to 42-52.In the closed-loop TCI group, propofol was administered using the closed-loop anesthesia delivery system to reach and maintain atarget BIS of 42-52.The BIS values would be recorded automatically by the system at each second after it began to run.The anesthesia duration, unconsciousness time, endotracheal intubation time, recovery time and endotracheal extubation time were recorded.The total usage of propfol and remifentanil were calculated.The incidence rates of emergence agitation, postoperative nausea and vomiting and intraoperative awareness were recorded.The frequencies of vasoactive drug were recorded.MDAPE, Wobble, GS through BIS values were calculated.Results BIS was maintained within ±10% of target (excellent) for significantly longer time in group C (52.1±10.5)% than that in group M (37.6±5.8)% (P<0.05).BIS was maintained within ±(10%-20%) of target (good) for the same time in both groups.MDAPE in group C (10.1±2.2)% were significantly lower than those in group M (15.3±6.4)% (P<0.05).GS in group C (23.1±8.9)% was significantly lower than that in group M (33.5±15.8)%.The usages of propofol in group C ·kg-1·min-1 were similar to those in group M (0.12±0.03) mg·kg-1·min-1, and the usages of remifentanil in group C (0.12±0.03) μg·kg-1·min-1 were similar to those in group M (0.15±0.05) μg·kg-1·min-1.The frequencies of vasoactive drug were similar in both groups.There was one incidence of emergence agitation in groups M.Postoperative nausea and vomiting and intraoperative awareness didn't occur in both groups.Conclusion The depth of the anesthesia is maitained more appropriately and stable in the closed-loop group than that in manual administration group.