Polyamide 6 (PA6)/organo-montmorillonite nanocomposites prepared by melt compounding using a co-rotating twin-screw extruder were intercalated nanocomposites. The modulus, bending strength and heat distortion temperature of these na.nocomposites increased with increasing clay content, and tensile strength increased up to 4.3 wt% and then decreased with further increases in montmorillonite content. The notched Izod impact strength decreased slightly with montmorillonite content. Nanocomposites based on the higher-molecular-weight PA6 yielded higher moduli, tensile strengths, and heat distortion temperatures at the same montinorillonite content. (C) 2004 Society of Plastics Engineers.