An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added to polymeric materials for improving their mechanical performance, using existing compounding techniques. The following items are discussed in particular, in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles during irradiation; (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultant nanocomposites; and (c) possible morphological changes induced by the addition of nanoparticles. Through irradiation grafting polymerization, nanoparticle agglomerates turn into a nano-composite microstructure (comprising the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn builds up a strong interfacial interaction with the surrounding, primary polymeric matrix during the subsequent mixing procedure. Due to the fact that different grafting polymers brought about different nanoparticle/matrix interfacial features, microstructures and properties of the ultimate nanocomposites could thus be tailored. It was found that the reinforcing and toughening effects of the 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 be controlled and broader applicability.