Objective To observe the clinical efficacy and safety of 2 differentdoses of dexmedetomidine combined with low-concentration ropivacaine during lumbar plexus block for elderly patients. Methods Ninety elderly patients were randomly divided into group A,B and C with 30 cases in each group. All patients were performed lumbar plexus block guided by ultrasound and nerve stimulator.35 mL of 0.25% ropivacaine was injected in group A,35ml of 0.25% ropivacaine plus dexmedetomidine 0.5 μg/kg in group B,and 35 mL of 0.25% ropiva-caine plus dexmedetomidine 1 ug·kg-1in group C. Onset time,duration,blocking extent and the occurrence of adverse events wererecordedafter lumbar plexus block.Ramssay sedation score,blood pressure,heart rate and res-piration were monitored intraoperatively,and the dosage of analgesic within 24 hours after operation was measured. Results Group C witnessed the shortest onset time of sensory and motor block and the longest duration,followed by group B and A(P<0.01).The Ramssay sedation score of group C was higher than that of group A and B(P<0.05),but no significant difference was found between group A and B. Group C witnessed the lowest blood pres-sure and heart rate(P < 0.05),followed by group A and B(P < 0.05). The dosage of analgesics in group C was less than thatof group A and B(P<0.05),withthe lest in group B(P<0.05).All patients in group B and C com-pleted the surgery only under nerve blockade.However,there were6 patients in group Arequiring additional intrave-nous anesthesia to complete the surgery for poor outcome of nerve blockade. Conclusions The mixture of 0.5~1 μg·kg-1dexmedetomidine and 0.25% ropivacaine in lumbar plexus block can achieve good anesthetic outcome for elderly patients,with moderate sedation,stable respiration and circulation,and less adverse events.