Mo-Sn-O systems were characterized by Raman spectroscopy and electrical conductivity measurements. The catalysts were obtained from precipitation of SnCl4 by ammonia in the presence of (NH4)(2)Mo7O24 using four different levels of Mo concentration. The electrical conductivity measurements showed that particles are formed by agglomeration of SnO2 crystals aggregated by polymolybdate. Raman spectroscopy suggested that four-coordinated species are dispersed at the external surface while six-coordinated species are inside the particles. For high Mo concentration (Mo > 10%), octahedral coordinated species are also on the surface. Bulk MoO3 oxide was not observed. These results confirm the model previously proposed.