Abstract: An operator-based robust nonlinear perfect tracking control for a manipulator with uncertainties was proposed by using operator-based robust right coprime factorization approach. The unknown uncertainties of the manipulator dynamics consist of the unknown modeling errors in measuring structural parameters of the robot arm and the external disturbances in real situations. Considering the unknown uncertain plant generates limitations in obtaining the tracking controller, an operator-based feedback control scheme was designed to eliminate the effect of uncertain plant. Then, a new perfect tracking condition was proposed for improving the trajectory of the robot arm. Finally, the effectiveness of the designed system was confirmed by simulation results.