Abstract Phase behavior of supercritical CO 2/styrene/poly (ethylene terephthlate) (PET) system was determined at 35°C and different pressures. The concentration of styrene in the fluid phase ranged from 0 to 1.3 mol/l. Styrene partitioned between the fluid phase and PET films, and significant amount of styrene was absorbed into PET matrix. When the styrene contained 0.3 mol% initiator azobis (isobutyronitrile) (AIBN), the mass uptake was higher than that of the styrene without the initiator because the AIBN initiated polymerization during the soaking period. It was found that considerable amount of styrene was carried out by CO 2 in the depressurization process. After the depressurization process, the PET films impregnated with styrene and AIBN were placed in a reactor and heated at 80°C for 4 h under the protection of N 2, and the PET/Polystyrene (PS) blends were obtained. The properties of the blends could be controlled by manipulating experimental conditions, such as soaking time, pressure and styrene concentration. The blends were characterized using IR, SEM, rheological measurement, and some mechanical properties were also determined. Rheometer study indicates that the presence of PS in PET can improve the mobility of PET.