The buck converter is one of DC/DC converters that are often used as power supplies. This paper presents parameter tuning methods to obtain circuit element values for the buck converter to minimize the output voltage variation under load changing environments. The conventional method using the concept of the phase margin is extended to have optimal phase margin that gives slightly improved performance in the output voltage response. For this, the phase margin becomes the tuning parameter that is optimized with the genetic algorithm. Next, the circuit element values are directly considered as the tuning parameters and optimized using the genetic algorithm to have very improved performance in the output voltage control of the buck converter.