In 11 cases of pectoralis major transfer, tracking movement was performed in the scapular and sagittal planes for both shoulder joints to compare the tracking movement ability of the operated shoulder and the unoperated shoulder. At the same time, electromyograms were taken of the upper trapezius, the middle deltoideus, the pectoralis major and the rhomboideus to compare the EMG amplitude of the operated shoulder and the unoperated shoulder. For all movement at average values, tracking movement ability was better in the operated shoulder. From these findings, it is thought that pectoralis major transfer increases shoulder stability at the time of movement. The increase in EMG amplitude of pectoralis major of the operated shoulder is considered to result from the action of the transferred pectoralis major, which serves as an effective abductor of the scapula, also taking into account the early occurrence of scapular abduction.