MoO3 thin films were fabricated in this work by the laser evaporation method operating in continuous wave mode. The samples were prepared at different substrate temperatures, in vacuum and at different oxygen pressures. Oxidation states of the films were obtained by X-ray photoelectron spectroscopy (XPS) and the crystalline structure was studied with X-ray diffraction (XRD). Morphological studies of the samples also were carried out using SEM. XPS measurements showed the presence of 3p bonds corresponding to the MoO3. Additionally some peaks associated to Mo-O and O-H bonds appear in the XPS-spectra. The samples prepared under 473 K substrate temperature presented XRD spectra proper of amorphous samples; above this temperature the samples shown polycrystalline phases mixed with α and β phases. A high homogeneity on the films surface can be seen in SEM images. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)