Abstract: Objective To compare the stress reactions in the old patients undergoing lower limbs replacement surgery in two groups treated with different doses of remifentanil, so as to optimize the dosage of remifentanil for the elderly.Methods Forty ASAⅡ-Ⅲpatients aged 65-75yr being scheduled for lower limbs replacement surgery were randomly divided into two groups(n=20 each):0.5μg/(kg·min)(L group)and 1.0 μg/(kg·min)(G group).MAP,HR,glucose and adrenalin were recorded at the points of time as before intubation(T₁), 5 min after intubation(T₂), 5 min after skin incision(T₃), 5 min after extubation (T₄)and 30 min after operation(T₅).And also recorded were extubation time and OOA/S.Results The weight, operation time,extubation time did not show statistical difference between the two groups. MAPs and HRs at T₄ and T₁ compared were of statistical difference within each group (P<0.05), but not between the two groups. The glucose values at T₅, T₃ and T₁ compared were of statistically significant difference in L group. The glucose values in L group and G group elevated gradually, but were in normal range. Adrenalin did not show significant difference in variation at the different points of time within each group or between the two groups. Statistically significant differences were shown in different doses of propofol and noradrenalin used in the two groups.Conclusion Remifentanil used in both groups proved to be able to attenuate stress reaction, and 0.5 μg/(kg·min) was the optimum dosage of remifentanil in the elderly undergoing lower limbs replacement surgery.