Tungsten oxide films were produced using reactive rf magnetron sputtering. In this work, nitrogen doping was used to modify structural and, optical properties of the material in the presence of two inert gases (argon and helium). Substituting helium gas with argon results in a decrease in the particle sizes and thus affects the band gap values. Bandgap values were obtained over the range of 2.43 to 3.01 eV via incorporating oxygen-nitrogen-argon/helium mixtures in the gas ambient. It was also observed that the atomic mass of the sputtering gas plays a major role for changing the primary crystallite size as well as the surface morphology and texture. © 2009 Elsevier B.V. All rights reserved.