In an attempt to elucidate the function of the interosseous membrane of the forearm, the anatomy of the interosseous membrane and the kinematics of the forearm during pro-supine movement were studied. Results and Conclusions; The rotation axis coincides with the line drawn from the ulnar head to the radial head. The motion of the radius is an arc of a circle about it. At one-fourth the length of the forearm from the distal end, the axis coincides with the edge of the interosseous border of the ulna. The most prominent fibers of the interosseous membrane are those being attached to this part. Therefore, tension of these most prominent fibers is constant. The interosseous membrane of the forearm apparently shows a structure meeting the needs for stabilizing two bones, transmitting thrusts and giving the origin to the muscles without interfering with the pro-supine movement of the forearm.