The nanostructure, morphology, and thermal properties of polyamide 6 (PA6)/clay nanocomposites were studied with X-ray scattering, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The wide-angle X-ray diffraction (WAXD) and TEM results indicate that the nanoclay platelets were exfoliated throughout the PA6 matrix. The crystallization behavior of PA6 was significantly influenced by the addition of clay to the polymer matrix. A clay-induced crystal transformation from the a phase to the 7 phase for PA6 was confirmed by WAXD and DSC; that is, the formation of gamma-form crystals was strongly enhanced by the presence of clay. With various clay concentrations, the degree of crystallinity and crystalline morphology (e.g., spherulite size, lamellar thickness, and long period) of PA6 and the nanocomposites changed dramatically, as evidenced by TEM and small-angle X-ray scattering results. The thermal behavior of the nanocomposites was investigated with DSC and compared with that of neat PA6. The possible origins of a new clay-induced endothermic peak at high temperature are discussed, and a model is proposed to explain the complex melting behavior of the PA6/clay nanocomposites. (c) 2006 Wiley Periodicals, Inc.