The crystalline orientation in nylon-6 and the crystalline and clay layer orientation in nylon-6/clay nanocomposites produced by 90 degrees equal channel angular extrusion (ECAE) are reported. A temperature of ca. 150 degrees C Was necessary to obtain the highest permanent shear strain for both nylon-6 and nylon-6/clay nanocomposites, the nanocomposites produced by either melt blending or in situ polymerization. Nylon-6 was found to affinely deform, while the introduction of the clay causes a nonaffine deformation of the crystal ellipsoids. By comparison of the orientation angle of clay layers from small angle X-ray scattering, the orientation angle of crystal ellipsoids from polarized optical microscopy, the calculated orientation angle from the apparent shear strain, and the main orientation direction of macromolecular chains, the mechanism of clay layer slip was proposed to explain the results of the high orientation of the macromolecular chains and the lagged orientation of the crystal ellipsoids in nylon-6/clay nanocomposite during ECAE process. The in situ polymerized nylon-6/clay nanocomposites achieved the highest orientation, which can be explained by the covalent connection of molecular chains and clay layers in this system.