In this paper, we present a study of the influence of the oxygen flow rate (phi) during r.f, sputtering of molybdenum metal targets on the resulting MoOx thin films. The optical behavior upon Li+ electrochemical intercalation (electrochromic effect) or UV irradiation (photochromic effect) is analyzed. At low phi, blue substoichiometric molybdenum oxide films are formed. At high phi, the composition of the oxide films approaches that of transparent, stoichiometric MoO3. The optical gap for the as-grown films increases with the increase of phi, in the range 2.8 eV for low phi to 3.2 eV at high phi. Lithium intercalation or UV irradiation promoted transmittance changes. The highest electrochemical and photochemical transmittance change was obtained for the sample deposited at low phi.