Abstract: Poly(ethylene terephthalate) (PET)/poly(ethylene-1-octene) (POE)/nano-SiO2 composites were prepared by a two-step melt blending process and then was foamed by a batch method with supercritical carbon dioxide as a foaming agent. The effects of nano-SiO2 and POE on the toughness and foaming behaviors of composites were investigated. The results indicated that the impact resistance of composites was enhanced significantly with the addition of nano-SiO2, and the impact strength increased by 150 % from 11.63 kJ/m2 to 29.15 kJ/m2 when 0.3 phr of nano-SiO2 was introduced. There is a synergistic toughening effect observed between Nano-SiO2 and POE. The storage modulus and complex viscosity of composites were found to decrease with an increase of nano-SiO2 content. Moreover, the cell size of composite foams was reduced from 75.39 to 50.49 μm with an increase of nano-SiO2 content from 0 to 1.0 phr, but their cell density increased from 6.67×107 to 9.61×107 cells/cm3 due to the heterogeneous nucleation effect of nano-SiO2.