We investigated the effect of anions to SERS of R6G on Ag nanoparticles to get deeper insight into the chemical enhancement. It was found that SCN - ion in addition to Cl - or Br - ions induced prominent activation (⩾10 2). It accompanied marked red-shift of the emission band from R6G indicating particular electronic interaction with the Ag surfaces. In contrast, SO32- and CN - ions quenched SERS due to their exclusive adsorption and partial dissolution of the nanoparticles. Accordingly, these phenomena are rationalized by distinct adsorption properties of the anions, as anticipated by equilibrium constants for the complexes formed with Ag + ions.