Disclosed are nano-sized metals and metal salts stabilized by using semi-telechelic and telechelic polymers prepared through living anionic polymerization, and their synthetic methods, and a nanostructure wherein the nano-sized particles are self-assembled by mixing block copolymers and film-casting. The present invention provides a new method for preparing nano-sized particles capable of easily accomplishing nanostructure by merely mixing, especially with block copolymers, and having excellent stability.