In this paper, we consider variable speed wind turbine systems containing uncertain elements. Though PI controller is generally used for pitch control, it cannot guarantee a stability and performance of the complicated wind turbine systems. A robust pitch control scheme is proposed to regulate the electric power output above the rated wind speed. The pitch controller is designed in order to guarantee uniform boundedness and uniform ultimate boundedness based on the bound values of the set where the uncertainties are laid or moves. In order to verify the proposed control scheme, we present stability analysis and simulation results using Matlab/Simulink.