Background: The purpose of this study was to evaluate the usefulness of the closed-loop system (STG-22; Nikkiso, Tokyo, Japan), a type of artificial endocrine pancreas for the continuous monitoring and control of intraoperative blood glucose in patients undergoing liver transplantation. Methods: Sixteen patients undergoing living-donor liver transplantation were enrolled in this study. Glucose levels were controlled with either a manual injection of insulin based on a commonly used sliding scale (manual insulin group, n=8) or a programmed infusion of insulin determined by the control algorithm of the artificial endocrine pancreas (programmed insulin group, n=8). The target glucose level range was set at 80-150 mg/dl. Results: The mean and SD of blood glucose concentration during surgery (Glu-Ave and Glu-SD, respectively) for the programmed insulin group were lower than for the manual insulin group. The coefficient of variability (Glu-CV=Glu-SD×100 /Glu-Ave) for the programmed insulin group was also lower than for the manual insulin group (20.1±4.9% vs. 26.9±6.1%; mean±SD). No hypoglycemia was detected in either group. Conclusion: The STG-22 closed-loop system is effective for maintaining strict blood glucose control during liver transplantation with minimal variability in blood glucose concentration. J. Med. Invest. 60: 205-212, August, 2013