Per-operative shivering following spinal anaesthesia is a common problem in the operation theatre. Adequate management of shivering during operation is one of the goals of anesthesiologists for the benefit of the patient. Because there are many unpleasant and harmful effects caused by shivering in many patients especially respiratory and cardiac disease patients. For this reason aggressive and optimal treatment of per-operative shivering is essential to reduce the morbidity of the patients. Our observations were that occurrence of shivering was more in younger patients than older patients, thin patients than obese patients, anxious patients than non-anxious patients and more frequent in patients who received vasoconstrictor drugs, administration of fluid at running rate just before or during operation, administration of cold local anaesthetic agents (by taking drug from the freeze) into subarachnoid space. And shivering was better managed by administration of nalbuphine HCl and surface skin warming (wrapping of the skin). There are many studies regarding the incidence, prevention & treatment of post-operative shivering but there is no study regarding the incidence & treatment of per-operative shivering by nalbuphine following spinal anaesthesia. This study was designed to compare the anti-shivering efficacy and side effects (Nausea, Vomiting, and Somnolence) of tramadol hydrochloride with that of nalbuphine hydrochloride in the treatment of per-operative shivering following spinal anaesthesia. This study was also done to observe the incidence of shivering during operation following spinal anesthesia.