Epoxy-clay nanocomposites were prepared by the dispersion of an organically modified layered clay in an epoxy resin (diglycidyl ether of bisphenol A) and curing in the presence of methyl tetrahydro acid anhydride at 80-160degreesC. The nanometer-scale dispersion of layered clay within the crosslinked epoxy-resin matrix was confirmed by X-ray diffraction and transmission electron microscopy, and the basal spacing of the silicate layer was greater than 100-150 Angstrom. Experiments indicated that the hydroxyethyl groups of the alkyl ammonium ions, which were located in the galleries of organically modified clay, participated in the curing reaction and were directly linked to the epoxy-resin matrix network. Experimental results showed that the properties of epoxy were improved, evidently because of the loading of organically modified clay. The impact strength and tensile strength of the nanocomposites increased by 87.8 and 20.9%, respectively, when 3 wt % organic clay was loaded, and this demonstrated that the composites were toughened and strengthened. The thermal-decomposition and heat-distortion temperatures were heightened in comparison with those of pure epoxy resin, and so were the dynamic mechanical properties, including the storage modulus and glass-transition temperature. Moreover, experiments showed that most properties of the composites were ameliorated with low clay contents. (C) 2003 Wiley Periodicals, Inc.