Background:- Spinal anesthesia is the most common anaesthesia technique for cesarean section. In this technique injection of a local anesthetic agent is injected into the subarachnoid space. The most common complication of spinal anesthesia is hypotension which is due to sympathetic blockade and activation of the Bezold Jarisch reex which leads to the utilization of higher doses of vasopressors for the maintenance of blood pressure. The present study was conducted to compare the effect of intravenous ondansetron premedication on spinal anesthesia-induced hypotension with normal saline. An observa methodology:- tional study was conducted in 180 term parturients of ASA - ІІ, scheduled for elective LSCS under spinal anesthesia. The patients were divided into two equal age groups: ondansetron 4mg (group O, n= 90) and saline group (group S, n= 90). Ondansetron 4mg (2ml) was given 10 min before the procedure in group O and group S received 2ml normal saline. Under all aseptic precautions, subarachnoid space was accessed through L3-L4 or L4-L5 intervertebral space using 25G Quincke's spinal needle. After conrmation of the free ow of CSF, a 2ml hyperbaric injection of bupivacaine 0.5% (Heavy) was administered in the subarachnoid space. Mean arterial pressure less than 65mmHg was considered as hypotension and treated with iv mephentermine 6mg bolus. The Occurrence of hypotension in Group O (22.22%) was signicantly l Result- ower than in group S(61.11%)(p<0.001). The MAP was signicantly higher in Group O at 2,4,6,8,10,12,14,16,20 and 25 minutes (p<0.005). 18 (20%) patients required one dose of mephentermine 6mg, and 2(2.22%) patients required two doses in group O. In group S 40 patients ((44.44%) required one dose of mephentermine 10 patients ((11.11%) ) required two doses and 5 patients (5.55%) required 3 doses. In group O 3 patients (3.33%) and in group S, 12 patients (13.33%) had nausea which was statistically signicant with a P value of 0.01. In group S 12 patients (13.33%) and 4 patients (4.44%) in group O had shivering. Which was statistically signicant with a P value of 0.03. Ondansetron is effective in Conclusion – preventing spinal-induced hypotension in elective cesarean section