Introduction: Spinal anesthesia is a simple, reliable, and most common anesthetic technique practiced worldwide. However, spinal anesthesia is associated with side effects such as hypotension, bradycardia, and shivering. Hypotension is most common intraoperative complication during spinal anaesthesia for caesarean section which has detrimental effects on both mother and fetus. Objective: To compare the effect of intravenous ondansetron with placebo for attenuation of spinal induced hypotension, change in heart rate, requirement for vasopressor and incidence of shivering and postoperative nausea- vomiting. Methods: A prospective randomised double blind study was conducted at Department of Anesthesia, Monno Medical College & Hospital, Manikganj, Bangladesh from July to December 2022. Total 100 patients belonging to ASA Class-I and II, aged 25-35 years, weight 40-60 kilograms, undergoing cesarean delivery under spinal anesthesia were included in this study. Group O (n=50) received 6mg ondansetron in normal saline intravenously; total volume made 10ml. Group S (n=50) received 10ml normal saline intravenously. Patient with history of PIH, convulsion, compromised airway or morbid obesity and required general anaesthesia for supplementation were excluded from study. Blood pressure and heart rate were checked every 5minutes till the end of the surgery. Data was analyzed by chi square test. Results: Total 100 patients were investigated for the effect of prophylactic ondansetron 6mg intravenously on fall in SBP, DBP and MBP, number of vasopressor boluses and total dose of vasopressor required. Distribution of cases according to age was comparable (p-0.339) in both groups (ondansetron group-25.27±3.62 and normal saline group- 24.63±3.60). In both groups maximum patients were below 25yrs old. We also studied the effect of ondansetron on the level of sensory height, duration of subarachnoid block to start of surgery, duration of surgery, heart rate, incidence of nausea, shivering and bradycardia. Systolic, diastolic and mean blood pressure were found to be higher in group O as compare to group S at different time intervals (p value < 0.05). In group O 66% patients required vasopressors whereas in group S 90% patients required vasopressors. Incidence of nausea and vomiting is less in group O (p-value=0.001). Conclusion: we conclude that prophylactic use of intravenous ondansetron prevent incidence of hypotension and less vasopressor is required to treat hypotension. Prophylactic ondansetron use is associated with less incidence of nausea and vomiting in spinal anesthesia in healthy parturient.