Background: The use of anesthetics and opioids leads to motor and behavioral inhibition, body movements and consequently a decrease in body temperature, which results in shivering. So, the objective of this study to evaluate the efficacy Of Ketamine and Ondansetron for prevention of shivering during anesthesia. Materials and Methods: Total 120 cases were included in this study. We were divided in to 2 groups. This study was conducted in the Department of Anaesthesia in Pacific Medical College and Hospital. Results: We were included 120 cases in this study. Among all 70 were female and rest were male. We were divided in to three group which were Ketamine (60) & Ondansetron (60). We were found in this study, the frequency of shivering in the groups who received Ketamine was significantly lower than the Ondansetron group. Conclusion: This study concludes that, Ketamine in dose of 0.25mg/kg has been found to be significantly more effective than ondansetron (4mg) during spinal anesthesia.