In this paper, a global sliding mode control (GSMC) scheme is implemented on a piezo-driven XY parallel micropositioning stage to compensate for the unmodeled hysteresis aiming at a sub-micron accuracy motion tracking control. The GSMC controller is designed with the consideration of all uncertainty bounds. In the controller implementation, a high-gain velocity observer is adopted to estimate the feedback velocity from the measured position. The effectiveness of the GSMC over ordinary SMC and traditional PID control is demonstrated through simulations, while the variations of design parameters on control performances are examined as well. Results show that the GSMC can reduce the hysteresis to a negligible level and lead to a sub-micron accuracy tracking with tolerance to some degrees of external disturbances, which provides a sound base of practical control of the microposition-ing system for micro/nano scale manipulation. © 2009 IEEE.