Abstract Background: Shivering is a common and unpleasant perioperative event following general as well as neuraxial anesthesia. It has been reported in 40-70% of regionally anesthetized patients. Shivering is a physiological compensa-tory response to core hypothermia precipitated by anesthetic induced thermoregulatory impairment, exposure to a cool environment, infusion of unwarmed fluids and evaporation from exposed surfaces. However, some shivering like tremors is not thermoregulatory. Aim of Study: To compare the efficacy of intrathecal dexmedetomidine versus intrathecal magnesium sulphate when added to hyperbaric bupivacaine for reducing the severity and incidence of post-spinal shivering in lower limb orthopedic surgeries. Patients and Methods: We compared the efficacy of intrathecal dexmedetomidine versus intrathecal magnesium sulphate for reducing the severity and incidence of post-spinal shivering in lower limb orthopedic surgeries. This study was a randomized controlled trial, 105 adult patients (ASA I-II) of both sexes, aged 18-45 years, were scheduled for lower limb orthopedic surgeries in Ain Shams University Hospitals. Patients were randomly allocated into three equal groups; each group consists of 35 patients and had spinal anesthesia with one of the following mixture: - In group A, spinal anesthesia was performed with 3.5ml of 0.5% hyperbaric bupivacaine (17.5mg), plus 5µg dexme-detomidine in 0.5ml normal saline. - In group B, 3.5ml of 0.5% hyperbaric bupivacaine (17.5mg), plus 25mg MgSO4 in 0.5ml normal saline was injected intrathecally. - In group C, 3.5ml of 0.5% hyperbaric bupivacaine (17.5mg), plus 0.5ml of normal saline was injected intrathecally. Results: Our results showed that all patients in the three groups were comparable regarding demographic data (includ-ing age, sex, weight and height) and intraoperative hemody-namics (SBP, DBP and HR). Regarding temperature, though difference in decreased core temperature was clinically insig-nificant, there was statistical significant difference between the three groups at almost all times as temperature at dexme-detomidine group was higher than magnesium group but the temperature at controlled group was lower than other two groups. Regarding shivering, we found that C group showed statistically significant higher number of total patients who developed shivering than B group and A group. 9 patients (25.7%) in dexmedetomidine group (group A), 12 patients (34.3%) in magnesium sulfate group (group B), and 20 patients (57.1%) in control group (group C). Conclusion: Our study viewed that intrathecal adminis-tration of dexmedetomidine or magnesium sulphate as adjuvant to heavy bupivacaine in spinal anesthesia, reduced incidence and severity of shivering in patients presented for lower limb orthopedic surgery with non-significant difference among both adjuvants.