The present invention provides a method of fabricating gold nanoparticles using electroless displacement plating, the method including the steps of: depositing on a substrate a metal having a reduction potential lower than that of gold to form a metal layer; and reacting a gold ion-containing plating solution with the metal layer. The invention also provides gold nanoparticles fabricated by the method. According to the method, gold nanostructures can be fabricated in a simple, cost-effective and efficient manner, and the fabricated gold nanoparticles can be used to measure surface-enhanced Raman scattering (SERS) signal or fluorescence. In addition, the invention enables the development of an optical sensor including the gold nanostructures.