In this paper, SnO2 nanoparticles were synthesized by the impregnation method with SnCl2 x 2H2O as the inorganic precursor and mesoporous silica MCM-41 as the hard template. The physical and chemical properties of the products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The SnO2 nanoparticles grew into the ordered channels of MCM-41. After removing the silica template, the products exhibited good rutile structure. The gas sensing properties of the SnO2 nanoparticles were also studied. The results indicated that these SnO2 nanoparticle sensors showed high selectivity towards ethanol.