FT-IR, FT-Raman and High Resolution NMR spectra of 3-phenyl-2-thiopyruvic acid (PTPA) have been measured in solution and in the solid state. Spectral assignments were carried out by referring to data of PTPA derivatives including para-substituted PTPA's, PTPA-d5and PTPA disulfide. All of the spectral evidences coherently point out that PTPA exists exclusively as the ene-thiol form both in solution and in the solid state. Detailed spectral features of PTPA were discussed in comparison with those of phenylpyruvic acid.