Nanocrystalline SnO 2 powders have been synthesized by two-step solid state reaction technique. Firstly, the brown SnO particles were obtained by grinding mixed SnCl 2 .2H 2 O and KOH powders at room temperature. Then, the powders were calcined in air (thermal oxidation) to form the SnO 2 nanoparticles. The phase compositions and microstructures of the product were examined by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), respectively. Furthermore, we have measured the gas-sensing property of the products and found its distinct selectivity towards ethanol at the presence of gasoline and acetylene, which is different from the property of pure SnO 2 nanoparticles. The mechanism of such a specificity was discussed briefly.