This paper reports an in situ Raman study of Cu electrodeposition from an acidic sulfate solution in the presence of bis-(3-sulfopropyl)-disulfide Na salt (SPS). In the absence of chloride, in situ surface-enhanced Raman spectra scarcely show few labile features in a narrow range of cathodic potential. When Cl- ions are added to the deposition bath, several features are clearly visible in the spectra, showing that SPS is adsorbed on the copper surface in a wide potential window during Cu electroplating.