Resol-layered silicate nanocomposites were prepared by the intercalative polymerization of phenol and formaldehyde in the presence of acid-modified montmorillonite (HMMT). The nanocomposites were studied by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic mechanical analysis (DMA), and rheological measurements. The exfoliation of HMMT was promoted by the intragallery reactions catalyzed by protons in the galleries of the clay, whereas the extragallery polymerization catalyzed by ammonia went on simultaneously. The nanocomposites showed higher glass-transition temperatures in the DMA diagram compared with the resol counterparts. The impact strength was improved significantly by the incorporation of the clay. (C) 2004 Wiley Periodicals, Inc.