Surface-enhanced hyper-Raman scattering (SEHRS) and surface-enhanced Raman scattering (SERS) have been employed to study phenazine adsorbed on the silver electrode surface at various negative potentials. It was observed that the scattering spectra of phenazine change drastically in frequencies and intensities with the change of applied potential, resulted from the electroreduction of phenazine (P) as the electrode potential moves negatively. The product of the electroreduction, 5,10-dihydrophenazine (PH2), as well as intermediate species, monoprotonated phenazine (PH+), phenazine semiquinone radical (PH.) and protonated semiquinone radical (PH2.+) have been detected by SERS. One of the intermediate species, PH2.+ radical, was also detected by SEHRS.