Polystyrene/montmorillonite nanocomposites were prepared by gamma-ray radiation polymerization. X-ray diffraction and high-resolution transmission electron microscopy confirmed that polystyrene (PS) could be easily inserted between the sheets of montmorillonite (MMT) to form intercalated nanocomposites. In these PS/MMT nanocomposites, the distance between the sheets of MMT was barely influenced by varying the content of the MMT. Thermal stabilities Of the samples were studied by thermal gravimetric analysis and differential scanning calorimetry. The glass-transition temperature of PS/MMT nanocomposites was obviously higher than that of the pure PS. (C) 2003 Wiley Periodicals, Inc.