Polyacrylonitrile (PAN)/Na-montmorillonite (Na-MMT)/SiO2 nanocomposites were prepared via in situ emulsion polymerization. X-ray diffraction (XRD) results suggest that the Na-NMT layers are exfoliated during the polymerization process. As evidenced by the transmission electron microscope (TEM), the Na-MMT and nano SiO2 particles exhibit good dispersion in the polymer matrix. It was found that the PAN/Na-MMT/SiO2 nanocomposites exhibit considerably enhanced mechanical properties compared with the PAN/Na-MMT and PAN/SiO2 nanocomposites. (c) 2005 Elsevier Ltd. All rights reserved.