A metal nanoparticle colloid solution, metal-polymer nanocomposites, and methods for preparing the same are provided. The metal nanoparticle colloid solution and the metal-polymer nanocomposites can be prepared with a variety of polymeric stabilizers and have uniform particle diameter and shape. The metal nanoparticle colloid solution and the metal-polymer nanocomposites have wide applications, for example, as an antibacterial agent, a sterilizer, a conductive adhesiv, conductive ink or an electromagnetic wave shielder for an image display.