The uncertain and random characteristics of wind energy make the problem of wind turbine control interesting and challenging. This work investigates an adaptive method for variable speed control of wind turbines under varying operation conditions. For fixed-speed operation of wind turbines, maximum power conversion can be achieved only at a particular wind speed, thus variable speed control of wind turbines is of practical interest in enhancing wind turbine operating efficiency over wide wind speeds. Based on the nonlinear dynamic model of wind turbine, adaptive algorithms are developed in accommodating unknown system parameter uncertainties. This method is shown to be able to achieve smooth and effective tracking of rotor angular speed to capture maximum wind energy. The effectiveness and adaptation of the proposed approach is validated via numerical simulation.