Separation of micrometer-size particles/cells based on physical/chemical properties is an essential process for various industrial/research applications, including the production of functional particles, biological experiments, and clinical diagnosis.Since the conventional techniques of particle separation like centrifugation, filtration, FFF, FACS, and MACS systems have limitations either in the separation precision or the availability, microfluidic devices are gaining attention as the new tools for particle separation, and researchers have developed microfluidic particle/cell sorters utilizing the stable laminar flows.We have proposed the concepts of purely hydrodynamic particle separation, named pinched-flow fractionation (PFF) and hydrodynamic filtration (HDF), in which particles are separated mainly based on size.Here we present several applications of these concepts for the highly-functional particle separation in microchannels.