This paper presents a systematic and comprehensive approach for differential mode (DM) EMI filter design in a three-phase boost-type power factor correction rectifier. Since the DM EMI filter forms a significant portion of the overall filter as well as converter volume, reduction of DM filter component size is kept as a major objective in the filter design process in order to improve the power density. In addition to the objectives of volume optimization and conducted emission attenuation requirement to comply with the EMI standard, the filter design process also ensures a near-unity power factor operation with the optimal set of EMI filter parameters. To accomplish this, the paper analyzes the effect of EMI filter component selection on the overall lower order (1-100 kHz) frequency response, which is important for evaluating the dynamic response and stability. The results from the proposed design approach are validated through simulation, the DM Bode plot, and frequency response of the input current with and without EMI filter. As a proof-of-concept verification, the proposed EMI filter is implemented in a 4 kW three-phase boost-PFC prototype, which demonstrates minimal phase displacement (<5o) of the input current.