Crosslinked polystyrene-multiwalled carbon nanotube (PS-MWCNT) balls, which act as conductive microfillers, were prepared by the in situ Suspension polymerization of styrene with MWCNTs and divinyl benzene (DVB) as a crosslinking agent. The diameters of the synthesized crosslinked PS-MWCNT balls ranged from 10 to 100 pm and their electrical conductivity was about 7.7 x 10(-3) S/cm. The morphology of the crosslinked PS-MWCNT balls was observed by scanning electron microscopy and transmission electron microscopy. The change in the chemical structure of the MWCNTs was confirmed by Raman spectroscopy and Fourier transform infrared spectroscopy. The mechanical and electrical properties of the PS/crosslinked PS-MWCNT ball composites were investigated. It was found that the tensile strength, ultimate strain, Young's modulus, and impact strength of the PS matrix were enhanced by the incorporation of the crosslinked PS-MWCNT balls. In addition, the mechanical properties of the PS/crosslinked PS-MWCNT ball composites were better than those of the PS/pristine MWCNT composites. (C) 2008 Wiley Periodicals, Inc. J Appi Polym Sci 110: 3737-3744, 2008