Fe-montmorillonite (Fe-MMT) was hydrothermally synthesized. It was modified by cetyl trimethylammonium bromide (CTAB) and successfully synthesized polystyrene/Fe-montmorillonite (PS/Fe-MMT) nanocomposites via bulk polymerization for the first time. The resulting nanocomposites were characterized by X-ray diffraction (XRD) spectra, transmission electron microscopy (TEM), high resolution electronic microscopy (HREM), thermal gravimetric analysis (TGA) and cone calorimeter. XRD, TEM and HREM indicated that both intercalated and exfoliated-intercalated structures were observed. In comparison with pure PS, the thermal stability was notably improved in the presence of clay. From cone calorimetry it was found that the peak of heat release rate (HRR) was significantly reduced by the formation of the nanocomposites. Also intercalated nanocomposites were more effective than exfoliated-intercalated nanocomposites in fire retardancy. (c) 2005 Springer Science + Business Media, Inc.