Vanadium dioxides ( VO_x) films were fabricated by reactive r. f . magnetron sputtering technique. Deposition rate, phase structure, surface morphology and transmittance in visible range of the films were characterized. Influence of oxygen / argon flow ratio on structure and optical properties of the films was investigated at same deposition air pressure. Results show that the flow ratio can modify the microstructure of the films, as oxygen / argon flow ratio increases, deposition rate of the films decreases while granular size as well as transmittance of the films increases.