In this article, the microstructures of polyethylene terephthalate (PET)/nanopowder of butadiene-styrene-vinylpyridine (BSV) rubber, PET/nanocalcium carbonate, and PET/nanoorganoclay as well as the effects of mechanical properties and crystallization on PET were investigated. Scanning electron microscope (SEM) indicated that when the nanoparticles are added into PET, small spheroidicity-shaped particles were seen in the SEM micrographs, and these particles were not nanopowders themselves. The crystallization of PET is improved with the incorporation of proper quantity of nanopowders of BSV and nanoorganoclay. Nanopowders of BSV and or organoclay can enhance PET's mechanical properties but not the nanocalcium carbonate. (C) 2009 Wiley Periodicals, Inc J Appl Polym Sci 113: 306-315, 2009