The optimal control problem is considered for nonliner systems affected by sinusoidal disturbances. A feedforward-PD optimal disturbance rejection control law based on output feedback of LQR is developed. By analysis the optimal disturbances rejection algorithms of nonliner systems based on time-domain state-space representation and the PD-control algorithms based on frequency-domain output feedback, the optimal PD tuning parameters are derived to achieve the purpose of optimal disturbances rejection. Finally, simulation results show that the algorithm is high in efficiency, easy to implement and well robust with respect to external sinusoidal disturbances.