The dc-dc buck converter is some of the most widely used power electronics circuit for its high conversion efficiency and flexible output voltage. These converter used for electronic device are designed to regulate the output voltage against the change of the input voltage and load current. This leads to the requirement of more advanced control method to meet the real demand .The controller offers advantage such as fixed switching frequency and zero steady state error and give a better small signal performance at the designed operating point but under large parameter and load variation their performance degrades so sliding mode control technique are well suited to dc-dc converter as they are inherently variable structure system .SM controlled converter generally suffer from switching frequency variation when the input voltage and output load are varied. A comparison of the effect of PWM controller and SM control of the dc-dc buck converter response in steady state under line variation and load variation is performed. The comparison with the PWM controller the SM control provides better steady state response, better dynamic response and robustness against system uncertainty disturbance. The converter with conventional sliding mode result in steady state error in load voltage.