Abstract: The Sol-Gel process and dip-coating technique were employed to prepare nanocrystalline SnO₂ and doped thin films using SnCl₄·5H₂O、Ce（NO₃）3·6H₂O、CuCl₂·2H₂O、La（NO₃）3·6H₂O and citric acid as the starting materials.The structure of thin films was characterized by XRD method.The effect of doping ratio on gas sensitivity of SnO₂ thin films was also studied.The result shows that under the same doping ratio, Ce³⁺ doped SnO₂ has the smallest grain-size, which is 9.5nm.When Ce³⁺、Cu²⁺、La³⁺ doping ratios are 4%, the gas sensitivities of those SnO₂ thin films to 64.50ppm ethanol are highest, which are 28.1、26.4、24.4 respectively.