Linear low density polyethylene (LLDPE)/montmorillonite clay (MMT) nanocomposites were obtained by dilution of a master batch containing 20.0% clay content in a twin screw extruder to obtain samples with 1.5-10.0% clay content. Samples were aged in fuel (ethanol or gasoline) for 30 days at room temperature (25 degrees C). In the present study, wide-angle X-ray diffraction (WAXD) showed that ethanol interacts with clay more than gasoline does, rearranging the clay structure that was lost during the preparation of the nanocomposites. Solid-state C-13 NMR spectroscopy showed that MMT modified the morphological structure of the LLDPE matrix, making it more heterogeneous. Moreover the fuel-aging process generates structures that are more heterogeneous than nonaged nanocomposites. Finally, fuel sorption analysis was used to verify the structure of the LLDPE matrix after the addition MMT. It was observed that the gasoline diffusion coefficients were higher than the ethanol diffusion coefficients.