Introduction & Objective: Post operative shivering is a prevalent complication of general and spinal anesthesia. Many drugs were used for prevention and treatment of shivering. The objective of this study was the comparison of clonidin, pethedin and fentanyl for treatment of post spinal anesthesia shivering.Materials & Methods: In this double blind randomized clinical trial, we compared the effects of 3 drug regimens to treat post operative shivering after spinal anesthesia in 60 elective caesarian sections with ASA class 1. Patients were divided into 3 groups (20 patients for each group). Each group received intravenously either pethedin 25 mg, clonidine 30 μg or fentanyl 50 μg. If a patient did not respond to the first dose, the same dose would be repeated up to a total of 3 times (with 5 minute intervals). Homodynamic changes, treatment responses and side effects were recorded. Then the resulting data were analyzed by SPSS software and chi-square test.Results: Considering control of shivering after first injection with pethedin 70%, clonidin 50% and fentanyl 30% with (p=0.04) major side effects in pethedin group were tachycardia 10%, nausea & vomiting 15%. In clonidine group the main side effects were dry mouth & drowsiness (16.7% & 3.3%) respectively. Fentanyl group had only 3.3% nausea vomiting accounting for the fewest number of side effects (p< 0.05). Homodynamic was stable in fentanyl & clonidine groups.Conclusion: We concluded that, clonidine offers better thermodynamics along with modest failure rate but pethedin was most effective with more serious side effects.