The mechanical properties of nylon-6/clay nanocomposites with variations in clay aspect ratio and orientation were studied. A large-scale simple shear process was utilized to alter the clay aspect ratio and orientation within the reference nanocomposite. It was found that the modulus, strength, and heat distortion temperature of the nanocomposites decreased as the clay aspect ratio and degree of orientation were reduced. Furthermore, the reduction of clay aspect ratio and orientation led to an increase in fracture toughness and ductility. The Halpin-Tsai and Mori-Tanaka micromechanics-based models were implemented to gain a better understanding with regard to the dependence of clay structural parameters, i.e. aspect ratio and orientation, on the reinforcement effect of the nanofillers. The micromechanical models can accurately describe the relationship between clay structural parameters and the corresponding moduli for exfoliated nanocomposites. (c) 2005 Elsevier Ltd. All rights reserved.