Tungsten oxide films have been deposited at room temperature from metallic tungsten target onto ITO coated glass substrate with sheet resistance of 15 V/Γ using reactive rf magnetron sputtering. The films formed in an Ar+2-25% O 2 gas mixture with total pressure of 10 m Torr and sputtering power 300 W. The films were subjected to electrochemical Li + insertion using in situ lithium triflate (trifluoromethanesulfonate) anhydrous solution. The electrochromic properties of the rf reactively sputtered tungsten oxide films have been investigated in relation to the oxygen concentration in the sputtering atmosphere. Transmittance measurements have been performed in situ during the electrochemical formation of the tungsten bronzes using Bruker IFS-66 Fourier spectrophotometer with integrating sphere. From the obtained results the best values of the electrochromic properties can be achieved at oxygen concentration of 15% with electrochromic parameters as, DT sol = 0.547, D(OD) s = 0.865, h s = 21.05 cm 2 /C, Q inj = 41.09 mC/cm 2 and Q lef . = 10.25 mC cm 2 respectively. The films deposited with oxygen concentration less than 5% were found in metallic state.