Objective To investigate the effect of dexmedetomidine (Dex) on postoperative pain in patients recieveing patient-controlled butorphanol.Methods Eighty patients (ASAⅠorⅡ) undergoing abdominal hysterectomy and general ansthesia were randomly devided into 2 groups;Dex group (group D,n=40)and control group(group C,n=40).Patients in Dex group were received Dex 0.6ug/kg（in 10 minutes） and control group were recieved normal saline respectively by pumped infusion one hour before the operation finished.All patients received a standadized butorphanol PCIA one hour before the operation finished, butorphanol 6mg in 100ml saline with tropisetron 5 mg,the loading dose was 0.5mg butorphanol,backgroud dose was 1ml/h,the controlled dose was 1ml/h,the lock time was 10minutes.The patients didn’t go back to the ward from the PACU,before their Aldrete score were less than 9 .The scores of VAS and RSS were recorded 1,2,6,12 and 24 hours after the operation finished,and the incidence rate of the nausea, vomiting and shivering were recorded too for 24 hours. Result There were no statistical significance between the two groups in the scores of VAS and RSS after PCIA.The consulmption of the butorphanol of the Dex group was less than the C group（p<0.05）.The incidence of postoperative nausea, vomiting and shivering in the Dex group was less than the C group（p<0.05）. Conclusion The patients in Dex group,received Dex 0.6ug/kg one hour before the operation finished,needed less consumption of butorphanol and manifested less postoperative nausea, vomiting and shivering.