Objective To investigate the effects of median effective dose (ED50 )of ropivacaine combined with sufentanil for spinal anesthesia in elderly patients.Methods Forty-eight elderly patients (ASAⅠ-Ⅲ)scheduled for elective lower limb or perineum operation under spinal anesthesia were enrolled in this study.All patients were randomly divided into two groups:control group (group C)and sufentanil group (group S).L3-4 intervertebral puncture was selected for all patients.Anesthetic solution in group C was 0.5% ropivacaine,in group S was 0.5% ropivacaine and sufentanil,which was fixed at 5.0 μg,based on the experimental results and sequential principle.The ropivacaine dose of first patient in the control group was 9.0 mg,and in sufentanil group was 8.0 mg,followed by reducing the dose of ropivacaine,each time 1.0 mg.If the patient appeared invalid standards response,the previous one was selected as the first case. ED50 was determined by Dixon??s sequential method.Results The ED50 of sufentanil combined with ropiva-caine for spinal anesthesia in elderly patients with lower extremity or perineal surgery was 6.40 mg (95%CI:5.98-6.80 mg),ED50 of only ropivacaine was 8.42 mg (95% CI:7.79-9.03 mg).Compared with pre-dose,MAP at 3,6,15 min after treated in group C were decreased,and lower than those in group S (P <0.01).Conclusion Combined with 5.0 μg sufentanil in spinal anesthesia for lower limb or perineal surgery elderly,median effective dose of ropivacaine is reduced.