Both poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) are biodegradable polymers, blending PLA with PEG is expected to toughen PLA matrix while maintaining its biodegradability. In this study, PLA/PEG blends in different ratios were prepared through triple-screw extruder, and the foaming behavior was investigated using supercritical carbon dioxide as physical blowing agent. The mechanical, thermal, rheological properties, and crystallization behavior were also studied. By the incorporation of PEG, the impact strength of the PLA/PEG blends improved by 98% with the specimens fractured in a ductile mode. The crystallization process of the blends was accelerated, and the crystallinity was significantly increased to 45.1%. The viscoelasticity of the PLA/PEG matrix was weakened, and the cells tended to break at the cell wall during cell expansion; thus, a highly interconnected structure with a maximum porosity of 82.3% was obtained. Moreover, the PLA/PEG blends exhibited higher cell densities and smaller cell size, compared to their neat counterparts. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3066-3073, 2013