Titania nanoparticles were prepared by means of two different synthetic procedures in order to obtain different particle size (diameter ranging from 20 nm to 350 nm), shapes and morphologies (amorphous or crystalline). Titania nanoparticles were surface modified with octadecylsilane in order to improve their compatibility with respect to polymeric matrices. High density polyethylene (HDPE) - titania nanocomposites were prepared by melt blending by using an internal mixer. The obtained nanocomposites were mechanically characterized and quasi static and creep tensile conditions. The presence of titania nanoparticles (1%vol) led to a significant increase of elastic modulus (20-25%) together with a slight increase of yield stress and a decrease of ultimate elongation. An interesting reduction of for both elastic and viscoelastic creep compliance components was also evidenced.