A SERS-active structure includes a substrate, at least one metal nanoparticle, a dielectric layer and a metal nanolayer. The metal nanoparticles are disposed on the substrate. The substrate and the metal nanoparticles are covered by the dielectric layer, so that the dielectric layer forms a recessed portion with a dihedral angle formed by a surface of the dielectric layer at which the at least one metal nanoparticle contacts the substrate. The dielectric layer is covered by the metal nanolayer and the metal nanolayer has a gap located at and exposing the recessed portion.