BACKGROUND Subarachnoid block is the preferred method of anaesthesia for caesarean section. Hypotension is the commonest side effects associated with spinal anaesthesia. 5–HT, a serotonergic receptor may be an important factor associated with inducing the Bezold–Jarisch reflex that may lead to bradycardia. AIMS AND OBJECTIVE To study the efficacy of Ondansetron for prevention of spinal anaesthesia induced hypotension in caesarean section primigravida individual and to investigate the administration of intravenous Ondansetron, a 5HT3 receptor antagonist, which could attenuate spinal–induced hypotension, bradycardia and shivering. METHODS AND MATERIALS The study was conducted in the department of Anaesthesia, IQ City Medical College, Durgapur West Bengal from February 2014 to March 2015. One hundred twenty parturient aged 25 to 35 years were scheduled for spinal anaesthesia and were divided randomly in to three equal groups. The control group received normal saline and intervention groups received 4 mg and 8 mg of intravenous Ondansetron 5 minutes before spinal anaesthesia. Mean arterial pressure (MAP), Heart rate (HR), bradycardia, shivering were recorded before and after spinal anaesthesia every 5 minutes during first 20 minutes of surgery. RESULT Demographic data were not statistically different among groups.HR was statistically different between the experimental groups and the control group. Six females (15%) in the in the control group had HR <50 bpm, that required intravenous atropine compared to experimental groups (p=0.02). In the control group 8 (20%) females had MAP <80mm Hg and required vasopressors compared to experimental groups (p=0.04). There were no significant differences in MAP and HR between the experimental groups (p=0.06). Incidence of shivering in the control group was 35% (14) that was statistically more than experimental group (p=0.02). CONCLUSION Administration of two different doses of intravenous Ondansetron 4mg and 8 mg significantly attenuates spinal induced hypotension, bradycardia, shivering compared to the control saline group.