Novel nanosize SnO2 particles were synthesized by a hard template method. The crystal structure and morphologies were characterized by X-ray diffraction and transmission electron microscopy. The particle size is around 4 nm, which is less than two times the depth (L) of the of the surface depletion layer. The sensing properties towards a series of gases, including ethanol, isopropanol, 1-butanol, formaldehyde, acetic acid, acetone, and 92# gasoline, were tested at different gas concentrations. The results reveal that the SnO2 nanoparticles have high responsivity towards forementioned toxic and flammable gases.