The miniaturization and weight saving of the boost converter for motor driving system of EV are very important issues for higher performance. This paper proposes the multi-phase boost chopper circuit for EV using coupled inductors which can achieve downsizing of inductors and the output smoothing capacitor. Coupled inductors enable to integrate magnetic components into one assembly. Therefore, the miniaturization and the lower cost of the magnetic component for the inductor are achieved. However, characteristics and design methods about integrated coupled inductors for proposed circuit have not been analyzed yet. This paper analyzes characteristic about the proposed circuit and flux in the core of proposed integrated coupled inductors. Moreover, the design procedure of proposed coupled inductors for the case of using the conventional three-leg core is presented. From experimental results, propriety of the design and effectiveness of the proposed circuit are confirmed.