This paper deals with the design and implementation of a composite nonlinear feedback law for a hard disk drive (HDD) with a dual-stage actuator, which consists of a voice coil motor (VCM) and a suspension piezoelectric microactuator. The VCM moves the read-write (RW) head of the HDD servo system to the target track while the microactuator is used to quickly settle the RW head at the target track. Thus, the VCM is a primary actuator and its control system is designed using a recently proposed composite nonlinear feedback control approach to have faster rising time and lower overshoot. The microactuator is a secondary actuator and is used to help the whole servo system to quickly settle at the target track. The microactuator is controlled through a second-order low pass filter, whose input signal is the tracking error of the VCM. Simulation and implementation results are presented and compared with those of a corresponding servo system with a single stage VCM actuator. These results show that the servo system with the dual stage actuator does yield a better performance compared to that of the system with a single stage actuator.