Acicular titania nanoparticles with average dimensions of 15 × 60 nm2 were produced by hydrothermal crystallization of TiOCl 2. Titania particles were surface-funetionalized with octadeeylsilane to obtain an organophilic surface. High-density polyethylene (HDPE) nanocomposites were prepared by melt compounding with 2, 3, and 5 vol % concentrations of untreated and surface-funcüonal-ized titania nanoparticles. Quasi-static mechanical tensile tests evidenced slight increments of both the elastic modulus and stress at yield, which were accompanied by a marked reduction of the strain at break at high filler contents. The introduction of titania nanoparticles induced a substantial reduction of the creep compliance of the HDPE matrix and of its creep rate, especially at long loading times. Untreated titania nanoparticles were more effective in reducing the creep compliance than the functionalized ones.