The electrochemical oxidation of propylene carbonate containing 1.0 mol dm(-3) LiClO4 was investigated with the aid of in situ Fourier transform infrared spectroscopy. The subtractively normalized interfacial Fourier transform infrared spectra were obtained for potentials ranging from 4.0 V vs. Li/Li+ to 5.0 V vs. Li/Li+. From these spectra it is concluded that propylene carbonate decomposes at more positive potentials than does 4.2 V vs. Li/Li+ on an Ni electrode. The decomposition products adsorbed on the electrode surface and then gradually dissolved in the electrolyte. From the spectral change for carbonyl groups, it can be seen that the ring opening reaction of propylene carbonate is included in the decomposition process of propylene carbonate electrolytes. On the other hand, the oxidation of propylene carbonate on Al, Pt, and Au electrodes was not observed in the range of potentials investigated. Thus, the oxidation of propylene carbonate containing 1.0 mol dm(-3) LiClO4 must depend on the electrode material. When the electrode surfaces were analyzed by x-ray photoelectron spectroscopy, those of the Ni and Al electrodes were found to be covered with their oxides, but oxides were not observed on the Pt or Au electrodes. It is therefore concluded that Ni oxide probably contributes to the decomposition of propylene carbonate.