Thin films of alpha-MoO3 were efficiently deposited on Si (100) by spin-coating of various precursor solutions i.e. ammonium heptamolybdate (HMA). citrate (CIT) and oxalate (OXA) complexes of Mo6+, and peroxo-polymolybdic (PER) solutions. The effect of the nature and concentration of the precursor and of the spin-coating rate were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The nature of the precursor used for the deposition influences the morphology of the crystals. For films obtained from CIT precursor solutions, an anisotropic morphology of MoO3 crystals with predominant basal faces is obtained, while MoO3 Crystals spin-coated from PER precursor solutions possess a more isotropic morphology. Films deposition from OXA and HMA precursors possess an intermediate morphology. Homogeneity and thickness of the films can be adjusted by tuning the concentration of the precursor solution and the spin-coating rate. Whatever the precursor used, the larger the crystals formed, the more developed were the basal faces obtained. (C) 2007 Published by Elsevier B.V.