An oxidation behavior of propylene carbonate with 1.0 moldm−3 LiBF4 or LiPF6 was investigated using in situ Fourier Transform Infrared (FTIR) spectroscopy with p- or s-polarized infrared beams to observe surface phenomena occurring on a LiCoO2 thin film electrode during anodic polarization beyond 4.0 V versus Li/Li+. The obtained FTIR spectra exhibited the formation of the same reaction products in two electrolytes during anodic polarization of the LiCoO2 thin film electrode. This result shows that the oxidation product of propylene carbonate is independent of the kind of electrolyte salt. On the other hand, the peak intensity in the FTIR spectra depended on the kind of electrolyte salt. This means that the decomposition rate of propylene carbonate is influenced by the kind of electrolyte salt. The oxidation of propylene carbonate with LiPF6 was more severe than that in propylene carbonate with LiBF4.