The interfacial behaviour of water molecules at a polycrystalline gold electrode surface in aqueous lithium, potassium and magnesium perchlorate solutions were investigated by in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). OH stretching absorption bands of water associated with anions or cations were observed, which showed almost no potential-dependent frequency shift in every solution. On the other hand, weak but relatively narrow bands were detected in 3500-3200 cm(-1) region, which apparently shifted toward lower frequencies with negative potential change (similar to 50 cm(-1)/V). We tentatively assigned these bands to modes of water molecules present in the Helmholtz layer.