The ASES (aerosol solvent extraction system) process, which is one of the SAS (Supercritical anti-solvent) processes, was used to fabricate the PS (Polystyrene) into nano-size particles. Dichloromethane (I)CM, CH2Cl2) and carbon dioxide were adopted as a solvent and as an anti-solvent for PS, respectively. SEM (scanning electron microscope) was used to observe the morphology and size of PS particles recrystallized by ASES process. The mean particle size and its distribution of processed particles were measured by using a laser diffraction PSA (particle size analyzer). In the ASES process, there are two key factors. One is atomization for fine droplets, and the other is mass transfer of droplets during precipitation in the vessel, which causes nucleation and growth of particles. They are affected by several elements such as temperature, pressure, concentration of solution, injection rate of solution and so on. The objective of this study was to investigate the effect of the various process parameters such as temperature, pressure, solution concentration and solution injection rate on PS particles. From this work, it was found that Polystyrene could be fabricated into submicron particles by ASES process using DCM as a solvent, and CO2 as an anti-solvent. And it was also found that the particle size was increased with increasing temperature, pressure and concentration of solution. And, by varying the solution injection rate, we found out that the solution injection rate is an important factor for making fine PS particles. (c) 2007 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.