Mo-SnO2 catalysts were prepared by SnO2.xH2O precipitation with ammonium heptamolybdate solution. Two Mo amounts were used: 5,5 and 14,5 percent (wt); Afterwards, these samples were impregnated with 1 percent Na (wt). These solids were characterized by nitrogen adsorption, UV-visible diffuse reflectance spectroscopy, temperature programmed reduction, X-ray diffraction, infrared spectroscopy of adsorbed pyridine and methanol. It was observed that the Na addition decreases the surface area of the Mo-SnO2 solids, caused by elimination of the micropores and the large pores of polymolybdates. It was also verified that Na promotes the agglomeration of Mo species, i.e. the amount of Mo dispersed species decreases and the polymolybdate one increases. Sodium also changes the solid acid properties: for the low Mo amount it was observed that Na promoted the formation of weak Lewis acid sites and the elimination of Brönsted sites; on the other hand for the high Mo amount, both Brönsted and weak Lewis acid sites content increased when Na was added. These results showed that sodium changed the texture, the Mo species and the acid properties of Mo-SnO2 catalysts.