Background: Postanesthetic shivering is a frequent complication of anesthesia, perhaps even aggravating pain especially during transurethral rsection of prostate (TURP) surgery. Objective: To compare the efficacy of I.V MgSO₄ and tramadol to placebo normal saline on incidence and severity of postspinal shivering in geriatric patients undergoing TURP surgery, when used as prophylaxis. Patients and methods: This was a comparative prospective study that included 39 geriatric male patients who scheduled for performing an elective TURP surgery under subarachnoid blockade (SAB) at Zagazig University Hospitals. Patients were divided equally into 3 groups: Group C received isotonic saline after spinal anesthesia, group Mg: received I.V MgSO₄ in isotonic saline and group T: received I.V tramadol in isotonic saline after spinal anesthesia. All patients were enrolled for examination before and after surgery. Results: There was no significant difference among the studied groups as regards HR, MAP and Spo2 between the three studied groups. Regarding changes in temperature between the studied groups, C group showed a significant lower temperature time followed by Mg group then T group at different times. There was a significant higher rate of shivering in C group then Mg group and the lowest was T group. Onset of shivering was significantly faster in control then Mg group and longer significantly in Group T. Conclusions: Prophylactic administration of I.V tramadol in a dose of 0.5 mg/kg immediately after SAB could significantly reduce the incidence and severity of postspinal shivering more than I.V MgSO₄ in a dose of 15 mg/kg in geriatric patients undergoing TURP surgery.