Objective To evaluate the efficacy and safety of dexmedetomidine aiding spinal -epidural anes-thesia for sedation.Methods Ninety ASAI -II female patients scheduled for elective spinal -epidural anesthesia were randomly divided into 3 groups(30 cases for each group)according to the digital table method.An epidural catheter was inseted at L2 -3 after satisfactory anesthesia,sedative drugs was intravenous.Group A received midazolam 0.05μg/kg initial loading dose for 10min and maintaining with 0.5μg·kg -1 ·h -1 .Group B received midazolam 0.06μg/kg for 5min and maintaining with 0.5mg·kg -1 ·h -1 .Group C received first intravenous injection of propo-fol 0.5 mg/kg,injection time 60s,maintaining with 0.3 -1.2mg·kg -1 ·h -1 .The infusion rate was adjusted to increase or decrease in order to maintain the desired level of sedation(Ramsay score of 3)during operation.The seda-tion efficacy and adverse reactions of three groups were compared.Results The onset time[(11.2 ±2.8)min]in group A was longer than that of group B[(6.4 ±2.4)min],group C[(5.0 ±2.1)min](t =7.12,9.70,all P <0.05).The offset time of group A,B[(12.3 ±2.4)min,(13.8 ±2.5 )min]were longer then those of group C [(7.4 ±2.3)min](t =8.36,7.95,all P <0.05).But 5 and 6 patients in the group B and C occurred hypoxia,and there were 8 and 9 patients developed partial airway obstruction due to relaxation of jaw muscle.At the time 30min, 60min and the end of surgery,the HR of the group A decreased deeply than the other two groups(t =5.02,4.92, 4.90,3.95,5.71,4.09,all P <0.05),10,5,6 patients were given atropine for increasing the HR in the group A,B and C respectively.Conclusion Dexmedetomidine is more safe and effective for the sedation of spinal -epidural an-esthesia,compared with midazolam and propofol,but with lower HR and longer onset time.