An irradiation grafting method was applied for the surface modification of titanium dioxide nanoparticles so that the latter can be added to polymeric materials for improving their mechanical performance. The modification of filler has been developed by coating this with an acrylate monomer, trimethylol propane triacrylate (TMPTA), followed by electron beam irradiation. Nanocomposites of polypropylene with different loading of unmodified and modified nano-fillers were prepared. The mechanical properties including modulus and tensile strength of the resultant nanocomposites are discussed as a function of filler loading. The composites with treated filler showed enhanced mechanical properties. It was found that the reinforcing effects of the treated nanoparticles on the polymer matrix could be fully brought into play at a rather low filler loading in comparison to conventional particulate-filled composites. Unlike the approaches for manufacturing of the other types of nanocomposites, including intercalation polymerization, the current technique is characterized by many advantages, such as simple, low cost, easy to control, and having broader applicability. Finally, experimental results were compared with theoretical predictions.