Mo/Al2O3 and W/ZrO2 systems have been studied in order to verify if the WO3+ZrO2 reaction occurs in solid state, and if the MoO3+Al2O3 reaction also occurs with porous alumina in the solid state. These mixtures were prepared using two Mo and W loadings: 5 and 10 µmolMo/m2 of support alumina and 10 and 16 µmolW/m2 of support zirconia, and they were calcined at 773 K. For Mo/Al2O3 systems three aluminas with different properties, such: specific area, porosity, hydroxylation degree, and OH groups distribution were used. For W/ZrO2 systems the effect of a higher treatment temperature: 973 K was also evaluated. All samples were characterized by the following techniques: X- ray diffraction, N2 adsorption, infrared absorption spectroscopy, and UV-vis diffuse reflectance spectroscopy. For Mo/Al2O3 systems it has been verified that molibdenum oxide reacted with the aluminas even though the mass transfer difficulties related to the porosity, forming Mo structures distinct from MoO3, which higher Mo dispersion may be related to more basic hydroxyl groups. For W/ZrO2 systems, the results have also shown that W species different from WO3 were obtained, and higher calcination temperature promoted the formation of more dispersed species onto the support.