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