The preparation of polyamide-6/clay, high-density polyethylene/clay, and high-density polyethylen/polyamide-6/clay nanocomposites is considered. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier Transform Infrared (FTIR) measurements show that the clay enhances the crystallization of the gamma-form of polyamide-6. The clay also acts as a nucleation agent and causes a reduction of spherulitte size. Scanning electron microscopy (SEM) analysis of fracture surfaces shows that the clay reduces the PA-6 particle size in the HDPE/PA-6/clay nanocomposites and changes the morphology. Mechanical properties and the effect of maleated polyethylene are also reported.