The structure of molybdenum oxocompounds formed in TiO2-supported MoO3 systems doped with alkaline metals have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) and X-ray absorption (XAS) spectroscopies. XRD, FT-IR, and XAS data give a detailed picture of the structure of molybdenum oxocompounds formed in these systems. Mo atoms are mostly octahedrally coordinated in an undoped TiO2 support, as a dispersed MoO3 phase. However, a high fraction of molybdenum cations are in tetrahedral coordination after the addition of Li, Na, or K as dopants. Thus, only MoO42- species exist in the 1 wt% Li-doped sample in the form of crystalline Li(2)MoO4, while tetrahedrally and octahedrally coordinated molybdenum form dispersed Mo2O72- chains in the 1 wt% Na- and K-doped systems. Octahedral polymolybdates, Rb2Mo3O10. H2O and Rb2Mo4O13, whose structures are based in [MoO6] units forming chains, are the species detected in the 1 wt% Rb-doped sample. Increasing the molybdenum content in K-doped samples favors formation of octahedral species, although in this case the structure of the supported phase is affected by the impregnation steps during the preparation of the sample.