Tourniquet induced hypertension occurs more frequently under general anaesthesia than regional anaesthesia and can be serious in patients with cardiopulmonary diseases, neurological disease and glaucoma. This study was a double-blinded randomized Control trial designed to investigate the effects of Clonidine, Dexmedetomidine and normal saline on prolonged tourniquet inflation. Material and Methods: Ninety patients scheduled for elective orthopaedic surgery of the upper limb under general anaesthesia were recruited. They were randomly assigned to receive intravenous Clonidine (1.0 mcg/kg; n=30) intravenous dexmedetomidine (0.5 mcg/kg; n=30), intravenous normal saline(n=30) 10 ml infused over a period of 10 min before tourniquet inflation. Arterial blood pressure and heart rate were recorded every 10 minutes until 90 minutes after the start of tourniquet inflation and again immediately after deflation. Result: In the Clonidine group, arterial pressure was not significantly changed, but in the Dexmedetomidine group arterial pressure was significantly increased at 20, 30, and 60 and 90 minutes after the start of tourniquet inflation. in the NS group arterial pressure was significantly increased at 40, 50, and 60 minutes after the start of tourniquet inflation. Development of more than 30% increase in arterial pressure during tourniquet inflation was more frequent in the group D and group NS than in the Clonidine group. Conclusion: Preoperative intravenous clonidine could therefore prevent tourniquet-induced hypertension in patients undergoing general anaesthesia.