The branches of the axillary nerve and branching pattern of the posterior cord of the brachial plexus are not fully described in the anatomy textbooks. The branching pattern of the axillary nerve is needed to understand various symptoms of quadrilateral space syndrome. We studied on the branching patterns and variation of the axillary nerve and posterior cord of brachial plexus in 127 adult cadaver arms. The axillary, radial and thoracodorsal nerves arising from the posterior cord of the brachial plexus were classified into 4 types according to the position of the thoracodorsal nerve. The most common type (42.5%) was that the three nerves directly arising from the posterior cord. The thoracodorsal nerve branched from the axillary nerve in 27.6%. The posterior branches of the axillary nerve were divided into 6 types by the arising point of the nerve to teres minor muscle. The deltoid branch and lateral superior brachial cutaneous nerve were divided after branching of nerve to teres minor muscle in 50.8%. The lower subscapular nerve was branched from the axillary nerve in 70.9%. We measured the distances from the branching point of the axillary nerve to the inferior border of the subscapularis in the quadriangular space and from the coracoid process to the axillary nerve. The length and motor point of the teres minor muscle were measured. The relationship of the axillary nerve and posterior circumflex humeral artery was observed. The axillary nerve was always medial to the artery and their superoinferior relationship was variable. The clinical significance of the branching pattern of the axillary nerve was discussed.