The purpose of this study was to evaluate the physical and chemical properties of engineering plastics processed using supercritical CO₂. First, we prepared disk-shaped test pieces via a general molding process, which were plasticized using supercritical CO₂ at temperatures lower than the glass-transition points of engineering plastics. Amorphous polymers were plasticized, and their molecular weight remained nearly unchanged after treatment with supercritical CO₂. The mechanical strength significantly decreased despite the unchanged molecular weight. The surface roughness and contact angle increased slightly, and electrical properties such as the rate of charging decreased significantly. These results suggest that supercritical CO₂ could be used for a new molding process performed at lower temperatures than those used in general molding processes, according to the required properties.