We report the case of a 64-year-old woman who had walked with the assistance of crutches all her life because of right leg paralysis caused by poliomyelitis during infancy. On examination, a tumor shadow was identified in her right axillary region. Thereafter, she developed numbnesss and pain in her right upper extremity. Contrast-enhanced computed tomography demonstrated a fusiform aneurysm of the right brachial artery measuring 25 × 22 mm with thrombotic occlusion. Good collateral circulation was observed via the anterior circumflex humeral artery that provided blood flow to the periphery artery. An elective surgery was performed due to the risk of rupture and thromboembolism. During the operation, we only resected the aneurysm and did not perform a bypass operation because the blood flow through the radial and ulnar arteries, based on the findings of a Doppler ultrasonic flow velocity distribution meter. Although a brachial artery aneurysm is rare, it can result in rupture and thromboembolism, and therefore surgical treatment should be considered for such cases.