We report the effect of inert gas (argon and helium) along with different concentrations of oxygen on the structural and optical properties of the rf magnetron sputtered nanocrystalline tungsten oxide thin films. The crystal structure and surface morphology were studied by X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. We find that the atomic mass of the sputtering gas significantly affects the primary crystallite size as well as the surface morphology and texture. We were able to relate the higher oxidation of the tungsten atoms with low partial pressure of oxygen when films are deposited in helium instead of argon. It was also observed that the bandgap of the WO3 films increases with increase in the partial pressure of oxygen. © 2008 Elsevier B.V. All rights reserved.