The mixed powders of poly(ethylene terephthalate) (PET) and SiO2 has been subjected to cryomilling. The evolution of microstructure with time was characterized using scanning electron microscope, transmission electron microscope, field emission scanning electron microscope, and laser diffraction particle size analyzer. It was shown that, upon cryomilling for 10 h, SiO2 nano particles were well deconglomerated into single particles (similar to 30 nm) that get homogeneously dispersed in PET matrix. The resulted PET/SiO2 primary particles were flake-shaped with a size of 400 nm. These primary composite particles agglomerated to form secondary composite particles with an average size about 7.6 pro. A three-stage model was purposed for the formation mechanism of the nanocomposite structures induced by cryomilling. Our evidences suggest that cryomilling is a capable and promising technique for the production of polymer/inorganic nanocomposites. (c) 2006 Wiley Periodicals, Inc.