Ｏｂｊｅｃｔｉｖｅ　To compare efficiency and safety of ultrasound guidance, nerve stimulation, and traditional blind methods in locating interscalene for brachial plexus blocking in patients with obesity.　Methods　A total of ninety patients with obesity, treated for upper extremity surgery in our hospital, were enrolled in this study. They were randomly divided into three groups (30 cases in each group). In these patients, the interscalene was located respectively by ① traditional method: search for the acupuncture point, ② nerve stimulation, triggering muscle contraction, ③ guidance of ultrasound. Brachial plexus block was performed by injecting 25 ml 0.375% ropivacaine hydrochloride into interscalene.　Results　The duration of surgery in three groups were similar (P>0.05). Sensory block developed faster and lasted longer in the group received ultrasound guidance than other groups (P<0.05). The satisfactory ratio of the sensory block under ultrasound guidance was 100%, significantly higher than that under nerve stimulation (83.3%) and traditional blind method (76.7%) (P<0.05). Complication occurred in only one case under ultrasound guidance, significantly lower than that in cases under traditional blind method(26.7%) and nerve stimulation (13.3%) (P<0.05).　Conclusions　Ultrasound guidance significantly improved the efficiency and safety of interscalene brachial plexus blocking.