Tungsten oxide thin films are of great interest due to their promising applications in various optoelectronic thin film devices. We have investigated the microstructural evolution of tungsten oxide thin films grown by DC magnetron sputtering on silicon substrate. The structural characterization and surface morphology were carried out using X-ray diffraction and Scanning Electron Microscopy (SEM). The as deposited films were amorphous, where as, thin films annealed above 400 degrees C were crystalline. In order to explain the microstructural changes due to annealing, we have proposed a "instability wheel'' model for the evolution of the microstructure. This model explains the transformation of mater into various geometries within them selves, followed by external perturbation. (C) 2009 Published by Elsevier B. V.