Structure of water at Pt/electrolyte solution interface was investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at ca. 3200cm(-1) and ca. 3400cm(-1), which are known to be due to the symmetric OH stretching (upsilon(1))of tetrahedrally coordinated. i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching (upsilon(3)) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively. The SFG intensity strongly depended on electrode potential. Several possibilities are Suggested for the potential dependence of the SFG intensity. (c) 2008 Elsevier Ltd. All rights reserved.