This work studied the morphology and physical properties of nanocomposites of different ethylene copolymers and functionalized polyethylenes with two different types of organoclays, to assess the potential application of these fillers as reinforcing components in the design of polyethylene and other polyolefinic based nanocomposites with enhanced properties. A polyethylene-grafted-maleic anhydride (PEMA), a poly(ethylene-co-acrylic acid), a poly(ethylene-co-vinyl acetate), and an ionomer of poly(ethylene-co-methacrylic acid) containing a small fraction of polyamide 6 were used to prepare nanocomposites by melt compounding in internal mixer. Two different types of commercial clays were used to obtain nanocomposites with the same organoclay content (5 wt %), i.e., an organomodified montmorillonite and an organomodified kaolinite. The morphology was evaluated by wide angle X-ray scattering, scanning electron microscopy, transmission electron microscopy, and optical microscopy. The thermal, mechanical and barrier properties were evaluated by differential scanning calorimetry and thermogravimetric analysis, tensile tests and oxygen transmission rate experiments, respectively. From the results, it was seen that PEMA and the ionomer are the best polymer matrices to disperse both organoclays under the conditions applied. Kaolinite and montmorillonite appeared to be dispersed in the nanorange, however, higher aspect ratio was observed for montmorillonite. The best improvements in thermal degradation and in mechanical reinforcement were shown for organomodified kaolinite nanocomposites. But the best improvements in thermo-oxidative degradation and in oxygen barrier were seen for the nanocomposites with organomodified montmorillonite. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1325-1335, 2010