Abstract: Polystyrene and poly (ethylene terephthalate glycol) (PS/PETG)blends were prepared by an internal mixer.PS and PS/PETG foams were prepared by the batch method using supercritical CO2 as the foaming agent.The rheological properties and cellular morphology were characterized by dynamic rotational rheometer and scanning electron microscope. The results showed that the addition of PETG has no significant effect on the rheological properties of PS ,but obvious effect on the cell size morphology of PS. The average cell diameter decreased from 22.68 μm to 7.58 μm and the cell density increased from 3.45×108cell/cm3to 4.47×109cell/cm3 when adding 10 % PETG into PS. The cell distribution also became narrow. Thus PETG can serve as the nucleation agent when blended with PS.