The operation and trade-off of Bridgeless Power Factor Correction (BPFC) circuit with interleaved Boost stages are investigated. By using interleaved BPFC, an overall reduction of the size of EMI filter can be achieved without increasing the switching frequency of the converter. And higher efficiency can be expected in interleaved BPFC through the universal line input comparing with traditional BPFC. Furthermore, an optimization procedure is implemented to improve system power density. Analysis and simulation results taken from a 3.5kW peak interleaved BPFC completed this paper.