Abstract INTRODUCTION: Subclavian artery thrombosis is a condition in which the blood flow through the vessel is suddenly obstructed. In fact, occlusion occurs in one of subclavian arteries, especially in the left subclavian artery. A patient with an acute occlusion presents with a cold, painful, cyanosis, pulseless upper extremity. CASE REPORT: A 48 years old lady admitted to Imam Khomeyni hospital (Sari, Iran) with a history of acute left upper limb pain. On examination, her left hand was cold, blue and painful on active and passive movements. Her left axilliary pulse was detected with no brachial or ulnar pulses. Left subclavian angiography showed a large thrombus in the proximal part of her left subclavian artery, the other sites of artery were normal. She had an elbow amputation in Tehran later. CONCLUSION: Therapeutic intervention is indicated in any symptomatic patient. Rapid diagnosis and treatment of thrombosis of subclavian artery prevent ischemia and gangrene of upper extremity. Subclavian artery thrombosis is uncommon cause of acute upper extremity ischemia, but should always regard to it. A true history and physical exam could be established rapid diagnosis and prevented side effects such as gangrene and amputation of upper extremity. Keywords: Acute thrombosis of Subclavian artery, Ischemia of upper extremity.