Ｏｂｊｅｃｔｉｖｅ　To evaluate the effect of dexmedetomidine（Dex） on postoperative pain in patients receiving patient controlled intravenous analgesia with dezocine after hysterectomy.　Methods　Sixty ASA Ⅰ or Ⅱ patients undergoing elective abdominal hysterectomy，aged 40 y-65 y，weighing 49 kg-75 kg were randomly divided into 2 groups （n=30）： group dezocine （group D）， group Dex and dezocine （group DD）. Dezocine 5 mg and tropisetron 2 mg were given in both groups at 10 min before the end of the operation. Patient controlled intravenous analgesia was performed with dezocine 30 mg+tropisetron 8 mg in 150 ml of normal saline after operation （background infusion at 3 ml/h with a bolus dose of 3 ml and a 15 min lockout interval）. Dex 0.8 μg/kg was given in 15 min in group DD by pumped infusion 30 min before the operation finished，while normal saline was given in group D. Viaual analogue scale（VAS）， Ramsay sedation scores， the number of patiengs requiring rescue analgesics and the number of pressing the patient controlled intravenous analgesia button were recorded at 4， 8， 24， 48 h after operation. Postoperative complications including nausea，vomiting，itching，bradycardia，hypotension，and respiratory depression were recorded.　Results　The VAS scores and times of pressing the patient controlled intravenous analgesia button were lower at 4 h and 8 h after surgery in group DD ［2（1-2）， 2（1-2）］ and ［1（0-1）， 0（0-1）］ than in group D ［3（2-3）， 2（2-3）］ and ［1（1-2）， 1（0-2）］（P<0.05）. The incidence of nausea and vomiting in group DD ［3%， 0%］ was less than the group D ［10%， 3%］ after surgery （P<0.05）.　Conclusions　Dex with a single dose of 0.8 μg/kg （given 15 min by pumped infusion） 30 min before operation finished can significantly improve the postoperative analgesic effect of patient controlled intravenous analgesia with dezocine with less adverse effects.