Poly(N-isopropylacrylamide)-b-[poly(ethyl acrylate)-g-poly(2-(diethylamino)ethyl methacrylate)] (PNIPAM-b-(PEA-g-PDEAEMA)) double hydrophilic graft copolymers were employed to prepare stable colloidal gold nanoparticles in situ with controllable size in aqueous media without any external reducing agent. PDEAEMA side chains served as reduction agent and stabilizer and PNIPAM segment acted as a hydrated layer to enhance the stability of gold nanoparticles. These gold nanoparticles showed a remarkable colloidal stability without any observable flocculation or aggregation for at least 2 months and they were characterized by UV-vis, XRD, TEM and AFM in detail. The size of gold nanoparticles can be tuned by adjusting the length of PDEAEMA side chains and the molar ratio of [DEAEMA]/[AuCl(4) over bar]. Both the increasing of the length of PDEAEMA side chains and the decreasing of [DEAEMA]/[AuCl(4) over bar] molar ratio resulted in the fall of size. (C)2009 Elsevier Ltd. All rights reserved.