The method for measuring a motorcycle trajectory using GPS is needed to make a simulation of motorcycle dynamics. In GPS measurement of a motorcycle, both declination of the body and obstacles near the course exert a bad influence. Therefore, we propose a new algorithm for GPS measurement of a motorcycle trajectory. We interpolate the missing observation data within a few seconds using curve of the second order, and use Kalman filter in positioning calculation. In the result, we succeeded in getting the trajectory with high accuracy, which is sufficiently continuous. The precision is equal to that of fixed point positioning given sufficient number of available satellites.