To prepare fine particles of PS(polystyrene), PMMA(poly (methyl methacrylate)) and PLGA(poly(DL-lactide-coglycolide)) by utilizing supercritical fluid as an anti-solvent, the experiments have been conducted at various temperatures, densities, concentrations and the ratios of linear velocity. The PS fine particles with various morphologies which include porous spherical fine particles with 2-10 μm pores have been prepared successfully. In the experiments for preparing porous PS particles a new concept of co-solute has been introduced, which might be utilized as an alternative method to produce porous polymer particles. In the case of PMMA the experiments have been performed by changing temperature, density, concentration, the ratio of linear velocity and the concentration of polymer solution. Since the flocculation and agglomeration are severe for PMMA, a new concept called co-antisolvent has been devised. The PMMA fine particles, which reduce flocculation greatly, have been produced by utilizing methanol as a co-antisolvent. In order to prepare fine particles of biodegradable PLGA all of the three injecting methodologies have been investigated. The nonporous particles, which have a little flocculation and sizes in the range of 50-100 nm, have been produced even at different experimental conditions. When the solvent dissolving PLGA has been changed to acetone/methanol(6:4), the coated network structure, which shows regular 0.5-1.0 μm pores, has been obtained. This network structure has a great potential to be utilized in the fields of controlled release and membrane separation technology.