A robust controller is proposed for mechanical and electrical servo system with unknown uncertainties and external load disturbances. This adaptive controller is made up of an Proportion- Integration-Differentiation(PID) controller and a Cerebellar Model Articulation Controller(CMAC). The PID controller is designed to stabilize the nominal model of the servo system, and the CMAC controller is designed to compensate for the system unknown uncertainties and external load disturbances. Simulation results demonstrate that the proposed controller has favorable tracking performance, and reasonable robustness for the uncertainties and external disturbances of the servo system.