Structural properties of motorcycle riders are discussed in this paper. First, locations of center of mass and moment of inertia are measured in normal and forward -leaned riding positions. Secondly, two kinds of rider models are proposed, which describe the mechanical motions of rider's body without his control actions. One of these models has two degrees of freedom concerning leaning motion of upper body and lateral movement of lower part. The other describes the yawing motions of upper and lower parts of body. The spring constants and the damping coefficients of human body included in these models are estimated by means of excitation experiments on riders.