This paper deals with (i) fabrication of microfluidic devices using living radical photo-polymerization method with various polymers (aromatic urethane diacrylate, photo-initiator, and photo-iniferter), and placement of porous plug using salt-leaching technique in microfluidic channel, (ii) determination of the pore size of the porous plug using flow field-flow fractionation, and (iii) investigation of separation of various particles including latex micro-particles and bacteria. It was demonstrated that the microfluidic device with porous plug could be used as a new and simple tool for particles (including microorganisms) separation based on their sizes and a miniaturized filter for water sample analyses.