Single spinal anesthesia in transurethral resection of bladder tumor (TURBT) has been reported to be unable to prevent obturator nerve stimulation and adductor muscle contraction, which can cause complications like bladder perforation. The present study aimed to compare the effectiveness of the classic and inguinal approaches for obturator nerve block (ONB). Seventy patients with cancers of the lateral wall of the bladder, scheduled to undergo TURBT at Imam Reza Hospital (Tabriz, Iran) during a 6-month period as of June 2016, were randomly allocated to groups of inguinal and classic methods (n=35). After the infusion of 500 mL of normal saline, spinal anesthesia was commenced using 3 mL (15 mg) of bupivacaine. Then ONB was performed using 10 mL of 1% lidocaine via the inguinal or classic approach in the inguinal group or the classic group, respectively. The success rate, defined as lack of post-block contraction with stimulation or during surgery, number of puncture attempts, time of block onset, and patient and surgeon satisfaction, was compared between the 2 methods using SPSS, version 19. The success rate of ONB was significantly higher in the inguinal group (97.1% vs. 71.4%; P=0.003). The number of puncture attempts in the classic group was more than that in the inguinal group (3.71±1.10 vs. 1.66±0.68, respectively; P<0.001). The block onset time was shorter in the inguinal group (1.5±0.66 min vs. 2.9±1.18 min; P<0.001). Dissatisfaction of the patient (19 cases vs. 2 cases) and the surgeon (10 cases vs. no case) was higher in the classic group (P<0.001).Compared to the classic approach, the inguinal approach for ONB appeared to be an easily performable, effective block with a high success rate, rapid onset, and good patient and surgeon satisfaction.Trial Registration Number: IRCT 201608171772N21