Low-density polyethylene/spherical silica (LDPE/SGS) nanocomposites, containing 1, 2, and 6 wt % neat and modified (having amine functional groups) silica nanoparticles, were prepared by melt mixing using a twin-screw corotating extruder. To improve the dispersion degree of the nanoparticles, glicydyl methacrylate grafted ethylene/n-octene copolymer (EOR-g-GMA) containing 0.6 wt % GMA was used as a compatibilizer. It was observed that mechanical properties such as tensile strength, Young's modulus, and impact strength increase and are mainly affected by the loading and size of silica nanoparticles as well as by the EOR-g-GMA. The addition of modified silica and EOR-g-GMA resulted in a further enhancement of mechanical properties due to the improved interfacial adhesion. Storage and loss modulus values of prepared nanocomposites measured by dynamic-mechanical thermal analysis were sensitive to the microstructure of the nanocomposites. Higher storage and loss modulus are evidence that the nanocomposites became stiffer. By adding the modified silica and EOR-g-GMA further increase in storage and loss modulus were observed due to the better dispersion of silica nanoparticles and increased compatibility between silica and the LDPE matrix. Both permitted a much more efficient transfer of stress from the polymer matrix to the silica nanoparticles. The improved barrier properties of all nanocomposites can also be mentioned as a positive effect. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012