---

Background: Postoperative shivering is a common problem with multiple complications. This study was compared effect of low doses of Ketamine with Pethidine for controlling postoperative shivering. Methods and Materials: This clinical trial was done on 189 elective cesarean section with ASA class I or II who had postoperative shivering. Patients with grade 2 or higher were divided in three groups and were injected 0.3mg/kg Ketamine and 0.5mg/kg Pethidine intravenously. In 5th and 10th minutes after injection, they were investigated for shivering intensity. Results: After 5 minute of injection drugs rate and intensity of shivering in Pethedine group was less than ketamine group. Ketamine with 0.5 mg/kg was more effective than 0.3mg/kg dose of it and Ketamine(p=0.041). In group with 0.5mg/kg dose of Ketamine, rate and intensity of postoperative shivering was more reduce than group with 0.3mg/kg of it in recovery(p=0/007). In Pethedine group rate and intersity of shivering was more reduce then 0.5mg/kg dose of Ketamine(p<0/001). This demonstrated that Pethedine is more effective than Ketamine. Conclusion: Although 0.5mg/kg dose of Ketamine has considerable effect on control of shivering but Pethedine is still a better choice for this side effect.