Abstract The structure of bisulfate anion adsorbed on a Pt(111) surface was studied by infrared spectroscopy as well as an ab initio molecular orbital calculation. The calculation predicted the structure and vibrational frequencies of the anion. The band assignments in the infrared and Raman spectra of KHSO4 were carried out by comparing the observed frequencies of the bisulfate anion with those of the calculated values. The single absorption band of bisulfate anion adsorbed on a Pt(111) surface showed a large frequency shift against a potential change (140 cm−1 V−1). The anion chemisorbed through tridentate oxygen coordination on the surface and the band was assigned to the symmetric SO3 stretching mode.