[Poly(2-(N,N-dimethylamino)ethyl methacrylate)]-b-poly(methyl methacrylate)-b-[poly(2-(N,N-dimethylamino)ethyl methacrylate)] (M = 45,000; 20K-5K-20K; PDI = 1.2) block copolymer surfactant stabilized amphiphilic gold-silver alloy nanoparticles (Au-Ag(PDMA-b-PMMA-b-PDMA)) has been synthesized in both water and in organic medium. The block copolymer stabilized pre-made alloy nanoparticles were successfully dispersed in hydrophobic poly(methyl methacrylate) homopolymer matrix (PMMA) of molecular weight 30,000. The successful synthesis of alloy nanoparticles was accessed by Transmission Electron Microscope (TEM), Energy Dispersed X-ray (EDX), and UV-visible spectrophotometric analysis. The surface functionality of the nanoparticles was confirmed by quantitative determining the grafting density of polymer chain around the nanoparticle surface using combination of thermo gravimetric (TGA) and TEM analysis. The hydrodynamic diameter of the alloy particles including the polymer chains was obtained from dynamic light scattering measurement (DLS). The mechanism of synthesis of high concentration of Au-Ag alloy particles from HAuCl4 and AgNO3 (in presence of Cl- from reduction of gold salt) metal particles precursors and the successful preparation of poly(methyl methacrylate)/gold-silver nanocomposite films have been discussed. CO 2007 Elsevier Inc. All rights reserved.