Polyamide 6/montmorillonite (MMT) nanocomposites were prepared by melt compounding method comprising 1-7.5 wt% of Nanomer I. 24 TL or 5 and 10 wt% of Cloisite 15A organically modified nanoclays. The composite samples were characterized by synchrotron X-ray, thermal and FT-IR spectroscopy methods looking for changes in the micro-and nanostructure of both PA6 matrix and MMT reinforcement as a function of the clay content and type. These data were discussed in conjunction with the mechanical properties of the respective nanocomposites. Generally, the Young's modulus was found to increase proportionally to the clay content being the highest in samples with strong aggregation of MMT at micron length scale. The tensile strength passed through a maximum at 2.5 wt% clay load presenting a homogeneous microstructure with almost no agglomeration. Increasing the amount of MMT produced less crystalline PA6 matrices, richer in gamma-PA6 polymorph and resulted in larger long spacings of PA6 due to expansion of both crystalline and amorphous domains. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3304-3315, 2011