Objective To evaluate the efficacy of preoperative femoral nerve block on preemptive analgesia in the elderly patients undergoing total knee arthroplasty under general anesthesia.Methods Sixty ASA physical status Ⅰ-Ⅲ patients of both sexes,aged 65-75 yr,scheduled for elective total knee arthroplasty,were randomly divided into 3 groups (n =20 each) using a random number table:control group (group Ⅰ),preoperative femoral nerve block group (group Ⅱ) and postoperative femoral nerve block group (group Ⅲ).Single-injection femoral nerve block was performed with 0.375％ ropivacaine 20 ml injected around the nerve under thc guidance of ultrasound immediately before induction of anesthesia and at the end of surgery in Ⅱ and Ⅲ groups,respectively.Patient-controlled intravenous analgesia (PCIA) with sufentanil (background infusion 2 ml/h,bolus dose 2 ml,lockout interval 15 min) was used until 2 days after surgery,and VAS score was maintained ≤ 3.When VAS score＞3,flurbiprofen axetil 50 mg was injected intravenously as rescue medication.The consumption of sufentanil per hour,requirement for rescue medication,and development of adverse reactions were recorded within 24 h after surgery.Sufentanil-sparing degree was calculated.Results Compared with group Ⅰ,the consumption of sufentanil per hour,requirement for rescue medication and the incidence of nausea and vomiting were significantly decreased within 24 h after surgery in Ⅱ and Ⅲ groups.The consumption of sufentanil per hour,requirement for rescue medication and the incidence of nausea and vomiting were significantly lower within 24 h after surgery in group Ⅱ than in group Ⅲ.The consumption of sufentanil per hour was decreased by 35％ in group Ⅱ as compared with group Ⅰ,and decreased by 18％ in group Ⅱ as compared with group Ⅲ.Conclusion Preoperative femoral nerve block can provide good preemptive analgesia in the elderly patients undergoing total knee arthroplasty under general anesthesia.