In rotational motion as forward, backward somersault and backward giant swing in horizontal bar, the center of gravity and moment of inertia for a given physical act of the human body were measured experimentally using the bifilar pendulum. The manner of change of the human body in motion was determined by a photographic method by using a 8-㎜ movie camera at the rate of 70 frames per second. 1. During angular motion in a somersault, the total angular momentum of the sustem remained constant unless an external net torque acts upon it. That is, the moment of inertia depends upon the distribution of the mass around its axis of rotation. This distribution is determined by the magnitude of the radius of gyration. The speed of rotation was inversely proportional to the radius of gyration. When the radius of gyration of a rotating body decreases, the angular speed of the body is proportionally increased. 2. The center of gravity determened in this pendulum gave experimental evidence that the whole body center of gravity acts as a projectile which travels a parabolic path in mid air. 3. In forward and backward somersault, the straight position had approximately two and one half times the moment of inertia in the tucked position.