Non-isothermal crystallization and the polymorphism of the PA6 and the polyamide 6/halloysite nanotubes (PA6/HNTs) nanocomposites are studied by adopting differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis and polarized optical microscopy (POM) observations. HNTs act as nucleating agent and accelerate the crystallization. The kinetics analysis indicates that the fold-surface free energy of PA6/HNTs nanocomposites is larger than that of neat PA6. The increasing tendency of the fold-surface free energy of PA6/HNTs nanocomposites is restricted at higher HNTs loading. interestingly, the crystallinity of the PA6/HNTs nanocomposites increases with cooling rate. HNTs content is found to have a significant effect upon the crystallinity of the PA6/HNTs nanocomposites, and the crystallinity reaches its maximum with 5 phr of HNTs content. Moreover. the higher HNTs content is. the larger percentage gamma-phase crystals take up. The crystallization behavior of the PA6/HNTs nanocomposites is correlated with the multiple roles of HNTs in the crystallization of PA6. (C) 2008 Elsevier B.V. All rights reserved.