Ｏｂｊｅｃｔｉｖｅ　To compare the effect of dexmedetomidine(Dex) with epinephrine as adjuvant to ropivacaine in supraclavicular brachial plexus block.　Methods　Sixty patients, ASA Ⅰ or Ⅱ, 44-68 years old, weight 50-75 kg, scheduled for fixation of Colle's fracture under ultrasound-guided supraclavicular brachial plexus block were divided randomly into three groups(n=20) with random number table, double-blinded fashion. In group C, 1 ml normal saline was used. In group D, 0.75 μg/kg Dex was diluted into 1 ml. In group E , epinephrine(100 μg) was diluted into 1 ml. The adjuvant was added to local anesthetic drug composed by 10 ml 1% hydrochloride ropivacaine and 10 ml normal saline. Onset time of sensory and motor block, duration of analgesia, onset time of postoperative analgesia was recorded in three groups. MAP, HR, SpO2, BIS and anesthetic complications were recorded in time points of before (T0) and 10 min (T1), 20 min (T2), 30 min (T3), 40 min (T4), 50 min (T5), 60 min (T6) after administration.　Results　The onset of sensory and motor block in group D are earlier than group C and E(P＜0.05). Duration of sensory block and motor block in group D and E were significantly longer than group C(P＜0.05). The needs for postoperative analgesia in D and E were postponed. The MAP in group D is lower than group C at T4-T5 and E at T3-T5(P＜0.05). The MAP in group E is higher than group C at T3(P＜0.05). Group D had lower HR than group C and E from T3 to T6(P＜0.05). The HR in group E is higher than group C from T3 to T5. Group D had significantly lower BIS score than group C and E since T2(P＜0.05).　Conclusions　Perineural 0.75 μg/kg of Dex has similarly ability of 100 μg epinephrine to enhance the quality and duration of analgesia in supraclavicular brachial plexus block. Dex has the ability to decrease cardiovascular stress and sedation, and should be a better adjuvant to local anesthesia in patients who are cautioned against epinephrine.