A 42-year-old female was admitted complaining of a pulsating mass of her left upper arm for two years. As she had played volleyball, she hit a ball with her upper arm accidentally for many times. The arteriogram showed a 30×35mm sized brachial artery aneurysm. Replacement of brachial aneurysm with saphanous vein graft was performed. Histologically, the aneurysmal wall consisted of three layers of arterial wall and had multiple breaks in continuity of the elastic layer. We diagnosed it was a true traumatic aneurysm caused by repetitive blunt injury. The causes and etiology of the brachial artery aneurysms were discussed.