New W-Mg-O systems have been obtained by impregnation of MgO with aqueous ammonium paratungstate solutions. The systems have been characterized by X-ray diffraction, Raman and W L-3 X-ray absorption (XAS) spectroscopies, FT-IR monitoring of pyridine adsorption for surface acidity, nitrogen adsorption at 77 K, and electron microscopy. Results obtained indicate that amorphous Mg tungstates are formed for low (723 K) calcination temperatures, but crystalline compounds are formed after calcination above 973 K. W6+ coordination in these solids depends on W content and calcination temperature. So, tetrahedral [WO4] species exist in amorphous species with low W content, and the crystalline ones obtained after calcination at 973 or 1073 K, while octahedral [WO6] species are present in amorphous solids with large (24 wt%) W content and in the crystalline phases formed after calcination at 1273 K, Formation of tungstates at rather low calcination temperature arises from the strong acid/base interaction between both reactants. Incorporation of tungsten leads to development of surface Lewis acid sites. The tungsten-containing species are less reducible in all cases than bulk WO3.