Nanocomposite formation of octadecyl amine treated montmorillonite clays in epoxy was investigated by small-angle X-ray scattering and atomic force microscopy. When diglycidyl ether of bisphenol A (DGEBA) was cured with equimolar or higher amounts of meta-phenylene diamine (MPDA), only intercalated nanostructures were obtained. Exfoliated nanocomposites were formed with DGEBA cured with less than stoichiometric amounts of MPDA or with auto-polymerization of DGEBA without curing agent. Extragallery crosslinking appeared to be favored with higher curing agent concentrations. Differential scanning calorimetry analyses of the exfoliated nanocomposites indicated that the reaction need not be complete in order to attain exfoliation in the DGEBA/montmorillonite mixture.