Optical property changes of reactively sputtered palladium oxide (PdOx) thin films during heating have been investigated by light transmission measurements and in situ Raman spectroscopy, combined with X-ray fluorescence and thermogravimetry analysis (TGA). The composition ratio and refractive index of as-deposited PdOx films varies depending on the oxygen gas-flow ratio during sputtering deposition. The transmitted light intensity at wavelengths of 405 and 635 nm measured during heating up to 1000 degrees C in air exhibits a sharp leap at 832 degrees C due to the thermal decomposition of PdO, and shows a gradual increase around 200-300 degrees C. The decomposition process of PdO is also measured by TGA as a significant weight loss of the sample. In situ Raman spectra of sputtered PdO, film obtained during heating up to 600 degrees C in air demonstrate that the crystallization of PdO starts above 200 degrees C and progresses during the whole annealing process. (c) 2006 Elsevier B.V. All rights reserved.