We have investigated the effect of the annealing time on the structural and abnormal optical changes of amorphous platinum oxide thin films on quartz glass substrate by do magnetron sputtering by using a pure platinum target. With increasing the annealing time, the decomposition phenomenon of a-PtOx, and the formation of Pt nanoclusters were also observed. X-ray diffraction and Raman scattering measurements confirmed that the change derives from the formation of Pt nanoclusters due to the thermal decomposition. A transmittance measurement of a-PtOx thin films annealed at 600 degrees C for 0-4 min demonstrated abnormal optical changes. (c) 2005 Elsevier B.V. All rights reserved.