Background: Spinal anesthesia-induced hypotension (SAIH) is a common complication during Cesarean sections. The prophylactic use of ondansetron has been suggested as a potential intervention to prevent SAIH. This study purposed to assess ondansetron efficacy in SAIH prevention and its impact on ephedrine consumption, as well as the incidence of adverse effects such as maternal bradycardia, postdural puncture headache, pruritus, and shivering. Methods: This prospective double-blind, placebo-controlled, randomized study was performed on female patients aged 18-35 years undergoing Cesarean Section under spinal anesthesia. The sample size was estimated using data from earlier research, with a total of 90 cases divided equally into two groups: the ondansetron group (Group O) and the placebo group (Group P). Baseline data, intraoperative monitoring, and postoperative assessments were conducted, and statistical comparison was conducted between the results of the two groups. Results: No substantial changes were seen between two groups regarding demographic data, anthropometric measures, American Society of Anesthesia (ASA) scores, and duration of surgery. However, the ondansetron group demonstrated a substantially lower hypotension incidence compared to the placebo group at various time points after spinal anesthesia. Additionally, the ondansetron group exhibited significantly higher systolic blood pressure and diastolic blood pressure readings, as well as a lower incidence of shivering, nausea, and vomiting. Conclusion: The prophylactic use of ondansetron was effective in reducing the incidence of spinal anesthesia-induced hypotension during Cesarean sections. It also resulted in less ephedrine consumption and a lower occurrence of shivering, nausea, and vomiting.