Tungsten was added to vanadium oxide films by RF magnetron sputtering and the effects of tungsten addition wereinvestigated. According to x-ray analysis, vanadium oxide films became amorphized by tungsten addition and the cycling reversibility was considerably improved. Electrochemical tests showed the cell capacity of about 60 ${mu}Ah/cm^2{mu}m$ when the amoung of additive tungsten reached 50 atomic percent. No appreciable degradation of the cell capacity could be observed after several hundred cycles.