We report a simple method to synthesize Ag, An, and Pt nanoparticles with a reasonable size dispersity using water-dispersible conducting polymer colloids composed of polyaniline (PANI) and conventional polyelectrolyte. This facile synthesis results in single crystalline metal nanoparticles that are stable in an aqueous solution for at least several weeks. The process involves incrementally adding a metal ion solution to aqueous conducting polymer colloids and does not require reducing agents such as NaBH4. In addition, the complete synthetic and purification procedure is carried out in an aqueous solution; therefore, it is environmentally benign and potentially suitable for large-scale production. We have also demonstrated synthesis of larger nanoparticles and nanosheets by varying the experimental parameters. With the tunable oxidation states of conducting polymers, we expect this synthetic platform can synthesize a wide range of nanostructured metals with specific size, shape and properties. Finally, the nanoparticles embedded in the conducting polymer matrix, the metal-polyaniline nanocomposite itself may be interesting since it represents a type of materials where metallic nanoislands are embedded in a semiconducting matrix. (c) 2005 Elsevier Ltd. All rights reserved.