We report a novel compounding process using Na-montmorillonite water slurry for preparing novel nylon 6/Na-montmorillonite nanocomposites. In this compounding process, the Na-montmorillonite slurry was blended with melting nylon 6 using an extruder, followed by removing the water. The Na-montmorillonite silicate layers were found to be exfoliated and dispersed homogeneously at nanometer level in the nanocomposites with an electron transmission microscope. The exfoliated Na-montmorillonite silicate layers were fixed in the nylon 6 matrix almost as they were in water. The nylon 6/Na-montmorillonite nanocomposites, loaded with only 1.6 wt% clay silicate layers, exhibited high strength, high modulus, high heat distortion temperature and low gas permeability compared to neat nylon 6. The properties of the nylon 6/Na-montmorillonite nanocomposites were nearly equal to those of conventional nylon 6/clay nanocomposites prepared by dry-compounding nylon 6 and organophilic clay ion-exchanged with alkylammonium ions. (C) 2003 Elsevier Science Ltd. All rights reserved.