Abstract: Objective To observe the anesthetic effect and safety of different doses of dexmedetomidine combined with ropivacaine for brachial plexus nerve block in children undergoing polydactyly surgery. Methods Eighty children undergoing polydactyly surgery were randomized into 4 groups to receive brachial plexus nerve block with dexmedetomidine at 0.25, 0.50 or 0.75 μg/kg combined with 0.25% ropivacaine (0.20 mL/kg) (D1, D2, and D3 groups, respectively) or with 0.25% ropivacaine (0.20 mL/kg) only (control group). The onset time, duration of brachial plexus nerve block, awakening time, success rate, and incidence of complications were compared among the groups. Results In D2 and D3 groups, the onset time and awakening time were shorter and anesthesia lasted longer than those in the control group. The onset time and awakening time were shorter and anesthesia maintenance time was longer in D3 group than in D1 group. The success rates of brachial plexus nerve block were significantly higher in D1-3 groups than in the control group (P<0.05). Hematoma was found in one of the patients. In each of the 4 groups, laryngeal nerve block occurred in 1 child and respiratory depression in another; 2 or 3 patients had Horner syndrome, and 1 patient in D3 group experienced an episode of lowered heart beat to below 70 min-1. All the complications were managed properly and the patients all recovered uneventfully. Conclusion Brachial plexus nerve block with 0.5 μg/kg dexmedetomidine combined with 0.25% ropivacaine (0.20 mL/kg) is safe for effective anesthesia in children undergoing surgery for polydactyly.