Objective　To provide anatomic evidence for the reconstruction of the opposition function by pectoralis minor transplantation.　Methods　Dissecting and surveying on the medial pectoral nerves and the deep branches of the ulnar nerves were performed. The number of myelinated ulnar nerve fibers was compared for confirming the possible nerve fiber suture during the operation.　Results　The medial pectoral nerve was the dominant fiber for the innervation of pectoralis minor muscle, which pierced into the pectoralis minor at the midclavicular line from the third intercostal space, with the number of myelinated fibers of about 868±130. Through medial intermuscular septum, the deep branch of the ulnar nerve respectively gave rise to conspicuous branches in the fourth and third spatia interossea metacarpi. The numbers of myelinated fibers of these branches respectively were 708±78 and  394±49. The number of myelinated fibers of the P3L4 was as many as that of the medial pectoral nerve and the recurrent branch of median nerve.　Conclusions　During the operational process of reconstructing the opposition function by pectoralis minor muscle transplantation, the medial pectoral nerve can be taken as the donor nerve, which should be found at the junction of the midclavicular line and the third intercostal space. It's more match with each other by suturing the P3L4 with the medial pectoral nerve.