The objective of this investigation is to determine the effects of montmorillonite layered silicates on the curing kinetics of an epoxy resin. Differential scanning calorimetry was used to probe the changes in reactivity due to the presence of montmorillonite and due to the diamine hardener. The enthalpy of polymerization was strongly affected at compositions greater than 5% (wt) montmorillonite for epoxy + montmorillonite reactions. On introduction of the hardener, epoxy + amine kinetics dominate the reaction for all compositions except for a montmorillonite concentration of 2.5 wt%. X-ray diffraction was used to determine if the reacted system was exfoliated. The results show a strong montmorillonite composition dependence on the exfoliated state. Transmission electron microscopy of the cured epoxies confirmed a mixed intercalated and exfoliated dispersion at compositions having montmorillonite greater than 2.5 wt%.