The aim of this work was to characterize the fracture behavior of polyamide 6 (PA6) and PA6 reinforced with clay (organically modified montmorillonite) [PA6/OMMT] at different temperatures and under higher loading rate. Pure PA6 and PA6 with different amounts and two types of OMMT were investigated. The structure and morphology of the nanocomposites were analyzed by X-ray diffraction technique and transmission electron microscopy. The fracture behavior was evaluated using the instrumented Charpy impact test at different temperatures starting from 30 degrees C up to 50 degrees C. To determine the fracture toughness KId at higher temperatures, the equivalent-energy concept was used. Based on the J-value versus temperature diagrams, the brittle-to-tough transition temperature TBTT of the materials was determined. It was found that the crack toughness as a function of temperature and the TBTT are influenced by the content of OMMT and the morphology. There are indications that at low OMMT contents, the deformation behavior is dominated by the matrix properties. With increasing filler content, the influence of the nanostructure on TBTT increases. The crack toughness of the nanocomposites with an intercalated morphology is higher than that of exfoliated ones, due to additional energy-dissipating mechanisms. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci, 2013