SUMMARYThe aim of this study was to develop a new evaluation method for controlling skill of a myoelectric control hand (MCH). Four amputees who daily used the MCH participated in this study. Measurement of two signals which were needed to control motion of the MCH was made. The two signals were assigned as the average rectified electromyograms of the forearm extensors and flexors. The values of the signals increased depending on the muscle contraction level. Therapy for using the MCH was performed to improve the ability to produce separate contractions of two muscles. This ability was defined as the skill in controlling the motion of the MCH. The skill in each motion was evaluated by the regression coefficient, which was calculated by the least squares method. The regression coefficient was inversely proportional to the skill. A quantitative index of skill can be provided by the newly developed method, and should be useful in developing efficient therapy to improve the skill in controlling the MCH.