Abstract: In this paper, Washout filter control technology is utilized to control chaos in pulse-width modulation (PWM) DC/DC converter. Firstly the disadvantages of Ott-Grebogi-Yorke (OGY) method which applied to chaos control in DC/DC converter system are discussed, and then the principle of chaos control scheme with Washout filter is shown by applying the mehod to a chaotic Hénon system. In the paper, Washout filter is applied to two kinds of PWM DC/DC converters, which have different control schemes, and translations from chaos to period in both of the converter systems are made. Theoretical analysis and computer simulation show that Washout filter method can work well and overcome the disadvantages of OGY method during controlling chaos in PWM DC/DC converters.