This article describes the clinical case of a 32-year –old female patient with an injured right little finger.When magnetic resonance angiography(MRA)of the right forearm was performed to detect the branch of posterior interosseous artery,the arterial variation of the right upper limb was found.The arterial anatomy of the left upper limb was normal.The radial artery arose from the axillary artery.The brachial artery continued to the ulnar artery in the forearm.The radial artery had a tortuous course.It was the medial branch of the axillary artery,and crossed the brachial artery from the medial to the lateral side in the distal third of the arm,then crossed the ulnar artery to the lateral side of the ulnar artery in the proximal third of the forearm.The clinical case of this arterial abnormality of the upper limb has not been previously reported.The knowledge on these variations is very useful for radiologists and surgeons.