In this paper, a non-linear control algorithm based on a sliding mode theory is proposed to maximize the power extraction of a variable speed wind turbine. This algorithm works in the partial load region. It has been used to control the wind turbine speed so that it reaches the desired value which corresponds to the maximum power point. In order to prove its efficiency, it has been compared with a classic linear control using a PI controller. Simulation tests are established using Matlab-Simulink The proposed MPPT algorithm presents good static and dynamic performances.