Objective: To compare the efficacy of prophylactic administration of Ondansetron before induction of spinal anesthesia with placebo, in preventing spinal induced hypotension. Patients and Methods: This Randomized Control trial was carried out at Holy Family Hospital, Rawalpindi from 29 April 2015 till 28 October 2015. A total of 106 patients were enrolled in the study. Patients in group A, received 6 mg Ondansetron. Patients in group B received normal saline. Mean arterial pressure (MAP) and heart rate (HR) were recorded every 5 minutes after performing spinal anesthesia. The study drug was considered efficacious if absence of hypotension for 20 minutes was recorded after inducing spinal anaesthesia. Data was analyzed using SPSS 17. Results: Hypotension occurred in 7.5% cases in Ondansetron group compared to 28.3% in normal saline group (p=0.005). Conclusion: Ondansetron is effective in preventing spinal induced hypotension. 
