Abstract: Epoxy/nano Si3}4 composites were prepared and their properties were investigated. The uni-form dispersion of nanoparticles in epoxy matrix was observed via TEM. When the loading of surface treated nano-Si3}4 was 3 wt%，the impact，tensile, and flexural strengths of the composites were in-
creased by 14S%,241%，and 2SS%，respectively; the electrical breakdown voltages under八C and DC were increased by 249%and 146%，respectively. The dielectric loss factor tan } and the dielectric constant s of nanocomposites were decreased.TG determination showed a better heat-resistance for the nanocomposites. The improvement in these properties was discussed with a model of "kernel- transition-al shell" structure.

Key words: epoxy resin, nano-silicon nitride, composite, mechanical property, electrical property