Abstract Background: Hypotension is one of the most common intra-operative complications associated with spinal anaesthe-sia. Its incidence in caesarean section has been estimated to be as high as 50-60%. Despite fluid preloading, lateral uterine displacement and the use of vasopressor agents. It occurs due to sympathetic block which leads to autonomic nervous system disturbances and a decrease in systemic vascular resistance. This can occur because the level of block must be at least at T4 to ensure adequate analgesia severe hypotension following spinal anaesthesia in caesarean section is a dangerous com-plication. If it is unnoticed or inadequately treated, it can lead to serious maternal or fetal compromise. Aim of Study: To evaluate the effect of two doses of prophylactic ondansetron on spinal anesthesia-induced hypo-tension and bradycardia among patients undergoing elective cesarean deliveries. Patients and Methods: This study was carried out in Ain Shams Hospital Obstetric Theatres from March 2020 to September 2020. Written informed consent was obtained from every parturient included in the study. Ethical approval for this study was provided by the Ethics Committee of Faculty of Medicine, Ain Shams University. FAMSU MS 155/2020 (FWA 000017585) 23/2/2020. Results: In our study, there is statistically significant difference between the studied groups regarding dose of vasopressor use. About 53.3% and 46.7% of those within ondansteron 4mg group received 10 and 12.5mg respectively. About 51.1% and 48.9% of those within ondansteron 8mg group received 12 and 15mg respectively. In terms of side effects, no patient within either group developed shivering, vomiting or bradycardia. Regarding nausea, there is statistically non-significant difference between the studied groups regarding occurrence of nausea. Conclusion: Prophylactic bolus of intravenous onandsetron 8mg and to a lesser extent 4mg could decrease the fall in the MBP of parturients following spinal anesthesia as well as ephedrine needed dose that could decrease neonatal acidosis associated with ephedrine use.