In this work, molybdenum oxide thin films were deposited by r.f. reactive sputtering of metallic molybdenum target in an Ar + O-2 atmosphere. Thin films with different compositions and crystal structures were obtained by varying the oxygen Row (phi). All samples, with the exception of the MoO2 film, showed an electrochromic behavior, due to the reversible Li+/e(-) insertion or extraction process. The transmittance change (lambda = 632.8 nm), for the best sample, was similar to 70%. The film having the best optical behavior is mostly formed by the beta -MoO3 phase. The composition, optical and mechanical properties were determined and analyzed in as-grown and in Li intercalated films. The local order structure was analyzed by X-ray absorption spectroscopy measurements at the Mo L-2,L-3-edges. The valence band was studied by Photoelectron Spectroscopy.