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 1.6wt% 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.