Objective To research the 50% effective anesthetic volume ( EAV50) of 0.5% ropivacaine in nerve stimulator-guided vertical infraclavicular brachial plexus block. Methods Thirty patients scheduled for forearm or hand surgery were blocked using 0. 5% ropivacaine in nerve stimulator-guided vertical infraclavicular brachial plexus block. The EAV50, which is the anesthetic volume corresponding to 50% success and 50% failure was determined by up-and-down sequential test. The starting dose of 0. 5% ropivacaine was 0. 55ml/kg. Block failure resulted in a dose increase 110% , and block success in a reduction 110%. The sensory and motor blockade were accessed at 5- min intervals (up to 60 min). Results In nerve stimulator-guided vertical infraclavicular brachial plexus block, EAV50 for 0.5% ropivacaine was 0.417ml/kg. In up-and-down sequential test, there were significantly different in the block success rates of lateral, medial and posterior cord ( P <0.01). Conclusion In nerve stimulator-guided vertical infraclavicular brachial plexus block, enough anesthetic volume must be given to increase block success rates of all the cords of brachial plexus, and EAV50 for 0. 5% ropivacaine was 0.417ml/kg.