Nylon-66 nanocomposites were prepared by melt-compounding nylon-66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 degreesC. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt-compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/ MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon-66 matrix were characterized by X-ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon-66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection-molded rectangular bar of nylon-66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection-molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near-surface layers and rotated themselves about the injection-molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon-66 was also investigated. (C) 2003 Wiley Periodicals, Inc.