Low nano-silica loaded polypropylene composites are produced by conventional compounding technique in which the nanoparticles are grafted by polystyrene using irradiation beforehand. A high interfacial stress transfer efficiency is demonstrated by both strengthening and toughening effects perceived in tensile tests. The role of the modified nanoparticles in improvement of tensile properties of the nano-composites is discussed in terms of percolation concept. A double percolation of yielded zones is presented to explain the specific influence generated by the nano-SiO2 particles at low-filler loading regime. (C) 2001 Elsevier Science Ltd. All rights reserved.