This paper presented the design methods of the boost inductor and the flying capacitors in the n-level FCBC in order to achieve passive components design optimization in terms of size reduction. The boost inductor is designed based on the maximum inductor voltage-time product parameter. Meanwhile, the capacitance of the flying capacitor is designed based on the maximum voltage stress specification on switching devices. The design methods are confirmed by the experimental results for the boost inductor and the flying capacitor in the three-level FCBC. The achieved maximum efficiency is 98.5% at the output power of 1 kW.