Background and Aims: This experimental study was designed to test the hypothesis that ondansetron, a selective 5-HT3 receptor antagonist, would decrease the duration of motor, sensory, and proprioception blockade in a dose-dependent fashion in a bupivacaine-induced sciatic nerve blockade. Materials and Methods: Forty-nine male Wistar Albino rats who underwent unilateral sciatic nerve block were divided into seven groups with an equal number in each group. Group B: only perineural block (PB), Group BO200: PB and perineural 200 μg ondansetron, Group BO400: PB and perineural 400 μg ondansetron, Group BO800: PB and perineural 800 μg ondansetron, Group BO800IP: PB and intraperitoneal 800 μg ondansetron, Group O800: only perineural 800 μg ondansetron, Group S: sham-operated. The rats' motor, sensory, and proprioception functions were evaluated by a blinded investigator every 10 min until they returned to normal function. The recovery times of the motor, sensory, and proprioception functions were recorded and compared. All sciatic nerves were removed and examined by electron microscopy for neurotoxic signs. Results: In which sciatic nerve block was formed with bupivacaine, the duration of the motor, sensory, and proprioception functions blockade was decreased, and the duration to return to normal functions was significantly shortened at Group BO800 (p < 0.05). According to electron microscopy results, perineural 200 μg, 400 μg, and 800 μg ondansetron were not neurotoxic. Conclusion: This is the first study showing that perineural ondansetron administration (800 μg dose) reverses the effect of the local anesthetics and shortens the duration of the motor, sensory, and proprioception functions blockade.