Pt island films were found to exhibit strong surface-enhanced IR absorption (SEIRA) when prepared under high-vacuum conditions and were applicable to SEIRA spectroscopy (SEIRAS) for in situ analysis of surface species during a heterogeneous catalytic reaction. SEIRA enhancement of Pt declined during storage in air due to a decrease in the bare Pt surface, which was caused by contaminations of the surface with organic compounds present in air, and increased significantly by heating at temperatures higher than 300 degreesC in air probably due to surface cleaning and morphological changes of Pt particles. The maximum enhancement was 32-fold as compared to attenuated total reflection IR spectroscopy. The detection range of Pt-SEIRAS was estimated to be the monolayer thickness of adsorbed n-decane. Pt-SEIRAS was applied to in situ observation of surface species during the photocatalytic oxidation of n-decane with O-2 on Pt/TiO2, and the results were discussed in comparison with those obtained for Au-SEIRAS.