DC-DC converters are widely used in the switched mode power supplies for its high conversion efficiency and flexible output voltage. Regulation problems of the DC-DC converters under variable load and parametric condition lead to the development of sliding mode controller. In this paper adaptive and non adaptive sliding mode controllers are implemented to control the output voltage of buck converter under variable load conditions. A suitable sliding coefficient is designed by deriving the state space representation of the buck converter and modified it to be adaptive to the loading conditions. It is observed that with the adaptive sliding mode controller, the output voltage not only remained constant for step overload but also reached the desired value faster. Adaptive sliding mode controller also saved the buck converter from entering into discontinuous mode under step under load condition.