We report a new strategy for synthesizing core–shell nanoparticles of Ag@SiO2 templated by a complex micelle of silver ions and a double hydrophilic block copolymer, poly[3-(methacryloylamino) propyl trimethylammonium chloride]-block-[2-(dimethylamino) ethyl methacrylate] (PMAPTAC-b-PDMAEMA). The obtained Ag@SiO2 core–shell nanoparticles have been successfully applied as a catalyst for the reduction of p-nitrophenol.