Metallocene polyethylene (mPE)/silica nanocomposites were prepared via melt mixing. Two types of commercial fumed nanosilica, bare silica (A200) and organic modified silica (R974), were incorporated to improve the mechanical properties of the nanocomposites. Transmission electron microscopy, atomic force microscopy, and scanning electron microscopy revealed that the modified silica was dispersed slightly better within the mPE matrix. No distinct effects on the thermal behaviors of the fast-crystallizing mPE matrix were observed with variations in both the silica dosages and types. Thermal stability was enhanced through the addition of nanosilica, with or without surface treatment. The surface-modified silica system showed slightly higher tensile strength and Young's modulus compared with the bare silica system, as evidenced by a rheological study using a Cole-Cole plot to assess enhanced polymer matrix-dispersed silica interactions, especially for high dosages of organic modified silica. A limited increment in the dynamic storage modulus for modified silica cases, completely opposite of that observed for bare silica cases, was due to the low-aspect ratio of smaller agglomerates from highly dispersed organic modified silica within the mPE matrix. POLYM. ENG. SCI., 51:434-444, 2011. (C) 2010 Society of Plastics Engineers