Background: Shivering is one of the most commonly encountered problems after both general and regional anesthesia and its incidence about 40% to 50% of the patients whom undergoing surgical operation under spinal anesthesia. The aim of this work was to compare two different clinically relevant doses of ondansetron (4mg vs 8mg) in prevention of postspinal anesthesia in inguinal herniorrhaphy. Patients and Methods: A comprehensive sample included elective unilateral inguinal hernia in Zagazig University hospitals during period of six months from November 2018 to April 2019 (10-11 cases / month) sample will be 63 cases randomly allocated into 3 groups; group A (ondansetron 4mg IV), group B (ondansetron 8mg IV) and group C (control group). Results: Each dose of ondansetron 4 mg or 8 mg have the ability to decrease the incidence of postspinal anesthesia with no significant differences between the two doses. There were no significant difference regarding side effects of the two doses of ondansetron in prevention of post spinal shivering. Conclusion: we concluded that both doses of intravenous ondansetron 4mg and 8mg are efficient and safe in reducing the incidence and severity of shivering during spinal anesthesia.