Sb-doped SnO2/SiO2 nano-composite thin films are prepared by sol-gel method. The surface topograph of the thin films is observed by atomic force microscopy (AFM). The optical properties of the thin films are studied by ultraviolet-visible spectra and p-polarized light reflectance angular spectrum. The results show that the crystalline grain size is about 35 nm, the specific surface area is large, and the duty porosity is high;the optical transmissivity is high, near 95% in visible spectrum range,and the optical band gap is about 3.67 eV. So Sb-doped SnO2/SiO2 nano-composition thin films is ideal candidate for optical gas-sensing. Further more, the gas-sensing test is made to three kinds of gas C3H8, C2H5OH and NH3, the results indicate, the doping of Sb to SnO2 films greatly improves the gas sensitivity to C2H5OH, and the gas sensitivity of Sb∶SnO2/SiO2 nano-composite thin films is higher than that of Sb∶SnO2 thin films.