Abstract: Objective To compare the effects of ultrasound-guided inguinal obturator nerve block and traditional nerve stimulator on preventing obturator nerve reflex. Methods Forty-eight patients with(American Society of Anesthesiology, ASA)ⅠorⅡaged 37-81 years who underwent transurethral electric excision of bladder tumor in our hospital from July 2011 to November 2012 were randomly divided into ultrasound-guided group(group U, n=24) and nerve stimulator group(group N, n=24). The bladder tumor was located in unilateral or bilateral obturator nerve-innervated area. Bilateral obturator nerve was blocked in 17 patients. The thigh adductor muscle strength in blocked side was measured before and after obturator nerve block. Frequencies of obturator nerve block puncture in each side, operational time, block success rate and complications were recorded. Results Each side was punctured once in group U, 18 sides were punctured once and 13 sides were punctured more than two times in group N(P<0.05). The operational time was significantly shorter in group U than in group N(P<0.05). No significant difference was found in the thigh adductor muscle strength and block success rate between the two groups before and after block(P>0.05). No local anesthetic toxicity, regional pain and obturator nerve injury occurred in two groups. Conclusion Ultrasound-guided inguinal obturator nerve block is more accurate, safe and effective in locating obturator nerve reflex than traditional nerve stimulator. Its frequency of puncture is less and operational time is shorter than traditional nerve stimulator.