The morphology and moisture barrier characteristics are studied of epoxy-based nanocomposites reinforced with layered silicates. Two different types of organoclay, including the quaternary alkylamine modified montmorillonite (KH-MT) and the octadecylamine modified montmorillonite (130P), were studied. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the 130P system exhibited a large increase in interlayer d-spacing from 3.39 mm to over 8 nm during the curing process, whereas the KH-MT system showed negligible changes in reflection angle and d-spacing, with the final interlayer distance of 3.39 nm after cure. The moisture absorption behaviour was different for different organoclays: the moisture absorption rate was similar for the neat polymer and the KH-MT system, which could be fitted to Fick's second law. The moisture absorption rate of the 130P system was much lower than the two systems, which was predicted using a non-Fickian model based on the ID Langmuirian solution. The deviation from the Fickian diffusion for the latter system is associated with exfoliated morphology and more uniform dispersion of clay particles, which altered the diffusion path of water molecules in the nanocomposite. The moisture diffusivity of nanocomposites in general decreased with increasing clay content, the reduction being more pronounced for the 130P system. The normalized permeability also showed a systematic degradation with increasing clay content, which agrees well with the prediction based on the tortuous path model.