At present, there are only a few researches on trajectory tracking control of the spherical robot using PID control algorithm, therefore, this paper deals with trajectory tracking problem of a spherical robot using adaptive PID controller. First, a desired velocity is obtained by a PI controller based on the kinematic model. Then, an adaptive PI controller based on the dynamic model with perturbations and uncertainties is presented for trajectory tracking control, and its stability analysis is given via Lyapunov Theory. The effectiveness of the proposed algorithm is illustrated based on the numerical simulation of a linear and a circular trajectory and the tracking performance of the proposed algorithm is shown compared with the existing PID controller. The proposed control method can be viewed as an attempt to the control problem of other similar underactuated mobile robots.