Poly(ethylene terephthalate) (PET)/silica nanocomposites were fabricated by direct polymerizing PET monomer dispersed with organic modified silica nanoparticles. The characteristics and properties of these nanocomposites were investigated by the transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. The results show that (1) the nanoparticles have been well dispersed in the polymer matrix; (2) the addition of nanoparticles can speed up the crystallization and melting point; and (3) the addition has no significant effect on the synthesis process. (C) 2003 Wiley Periodicals, Inc.