Objective To investigate the changes in BIS values induced by TCI of sufentanil at different target concentrations (Cr) during propofol anesthesia. Methods Fifty ASA Ⅰ or Ⅱ patients aged 18-57 yr undergoing elective surgery under general anesthesia were randomly divided into 5 groups (n = 10 each) based on CTof sufentanil: 0.07, 0.10, 0.14, 0.20 and 0.28 ng/ml. BIS, ECG, HR, MAP, SpO2, PET CO2 were continuously monitored. Anesthesia was induced with propofol TCI. The initial target plasma concentration (Cp) was set at 3.0 μg/ml. If the patient remained conscious 5 rain after the equilibrium between Cp and target effect-site concentration (Ce) was achieved, the Cp of propofol was increasing in increments of 0.3 μg/ml until consciousness was lost (LOC). Propofoi TCI was maintained at this level and Cp and Ce were recorded. TCI of safentanil was then started at the different Cp set in the 5 groups. When the equilibrium between Cp and Ce of safentanil was achieved, tracheal intubation was facilitated with succinyl choline 1.5 mg/kg and the patients were mechanically ventilated (VT= 8-10 mi/kg, RR = 8-12 bpm, PETCO2 = 30-35 mm Hg). BIS value, HR, MAP, SP and DP were recorded before induction of anesthesia at LOC (T0) and 1,2, 3, 4, 5 and 6 min after sufentanil TCI was started. Results There was no significant difference in Cp and Ce of propofol at LOC (T0) among the 5 groups. BIS value was decreasing after the beginning of TCI of sufentanil and was significantly lower than the BIS value at T0. The changes in BIS value was negatively correlated with the Cp and Ce of sufentanil. Conclusion TCI of sufentanil can decrease BIS value further during propofol anesthesia.