Abstract: Objective To study the effective remifentanil plasma concentration (EC₅₀) for inhibiting hemodynamic response to tracheal intubation in 50% elderly patients when propofol anesthesia was guided by bispectral index (BIS). Methods Twenty-six ASAⅠ-Ⅱelderly patients at the age of 65-78 years admitted to our hospital from March 2012 to June 2012 for surgery within 2 hours after admission were included in this study. The patients received target-controlled infusion of 3 μ g/ml propofol. The plasma target concentration of remifentanil was preset at 4.0 ng/ml for the first patient whose target plasma remifentanil concentration was decided according to the Dixon's up-and-down sequential allocation. Results No significant difference was found in BIS value before and after tracheal intubation. The EC₅₀ of remifentanil to inhibit the hemodynamic response to tracheal intubation was 1.93 ng/ml and its 95% CI was 1.63-2.23 ng/ml according the Dixon's up-and-down sequential allocation. Conclusion Remifentanil at the concentration of 1.93 ng/ml can effectively inhibit the hemodynamic response to tracheal intubation in 50% elderly patients when the concentration of propofol is maintained at 3 μ g/ml.