Epoxy-clay nanocomposites were synthesised using two montmorillonite clays (MMT) with different cation-exchange capacities (CEC) (94 and 140 meg/100 g). The purpose was to investigate the influence of the CEC of the clay on the synthesis and structure of epoxy-clay nanocomposites. The dispersion of the 1 nm thick clay layers was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Although XRD data did not show any apparent order of the clay layers in the nanocomposite, TEM revealed parallel clay layers with interlamellar spacing of 90 Angstrom (MMT of high CEC) and 110 Angstrom (MMT of lower CEC) and the presence of remnant multiplets of non-exfoliated layers. A mechanism responsible for the influence of CEC on nanocomposite interlamellar spacing is discussed. The dispersion of the clay was investigated by SEM and found to be finer in the nanocomposites as compared with in conventional composites although the nanocomposites still have clay aggregates at the microscale rather than a monolithic structure.