This randomized double blind study was conducted to know the efficacy of ondansetron as prophylactic agent for reduction in incidence of hypotension and bradycardia in patients undergoing caesarean section under spinal anaesthesia. Methodology: 60 ASA 1 & 2 patients were divided randomly into two groups(saline and ondansetron ) having 30 in each group. Saline group was administered with 10 ml of saline IV and ondansetrongroup received Ondansetron 4mg(10ml) 5 mins before spinal anaesthesia.Heart rate, systolic, diastolic & mean blood pressures were recorded at the time of spinal drug administration and at 2 mins interval upto 20 mins, followed by 5 mins interval until end of surgery. Results: There was significant reduction in systolic, diastolic and mean BP in saline group compared to ondansetron group. But the heart rate in both the groups was comparable. Conclusion: Prophylacticondansetron decreases incidences of hypotension after spinal anaesthesia in caesarean section.