In this study, we demonstrated an in situ FTIR measurement for an electrochemical oxidation of propylene carbonate with 1.0 mol dm(-3) LiClO4 on LiCoO2 cathode active material used in rechargeable lithium batteries. A thin film electrode of LiCoO2 was prepared by an r.f. sputtering method. The prepared LiCoO2 film had high quality as an electrode for the in situ FTIR measurement as well as a cathode material. The FTIR spectra were obtained at various electrode potentials ranging from 4.1 to 4.8 V vs. Li/Li+. Peaks corresponding to decomposition products of propylene carbonate show that the electrochemical oxidation of propylene carbonate was assigned to some compounds having carboxylic groups and carboxylic acid anhydrides. Several peaks attributed to propylene carbonate were also observed, indicating that propylene carbonate was adsorbed on the LiCoO2 thin film electrode surface before the anodic polarization.