Analysis of the function of the foot is expected to understand walking or jump motion, or to evaluate foot illness quantitatively. Especially, it is well known that the arch of the foot has an important role (e.g. shock absorbing). However, generally, it is difficult to measure in vivo information (e.g. bone, muscle, vinculum) during dynamic motion, because of the limitation of the measurement system (CT, X-ray image). In this presentation, I propose a three-dimensional analysis method for the arches of the foot based on an optical motion capture data. The arch deformation is evaluated by an ellipsoidal approximation which is calculated from marker position. I validate the proposed method by comparison with bone movement which is calculated from X-ray TV system image. The result of the comparison indicates that the proposed method can reflect in vivo bone movement. Also, I apply the proposed method to analysis of three dynamic motion, fallen, lift up, walk. These results indicate that the proposed method is useful for the arch deformation analysis.