One of the unpleasant side effects of general anesthesia is shivering in the process of recovery. It is an involuntary oscillatory mechanical movement that can be classified as clonic movements. These movements can affect one or several groups of skeletal muscles beginning from 5 to 30 minutes after the discontinuation of anesthesia.We aimed to study ketamine's effect on shivering after operation compared to pethidine as a way for treatment of postoperative shivering.In this study, 60 patients who underwent ENT surgery with general anesthesia and had shivering during recovery were randomly divided into two groups of 30 patients each receiving ketamine (0.2 mg/kg IV) and pethidine (0.5 mg/kg).There was no statistically significant difference between the shivering intensity in both groups. Only regarding the shivering in the first minute after entering the recovery room, there was an obvious difference between ketamine and pethidine groups which was again not statistically significant (P = 0.07).The results of this study showed that ketamine and pethidine are both equally effective in the reduction of postoperative shivering.