The In-Sn oxides composites made up of nanoparticles were successfully synthesized by an environment friendly one-step hydrothermal approach. The structures and morphologies of the composites were investigated by different kinds of techniques, including X-ray diffraction, field-emission electron scanning microscopy, transmission electron microscopy, electrochemical workstation and H-2-TPR technique. Their gas sensing performances of In-Sn oxides composites toward ethanol were investigated using a static system and possible gas-sensing mechanism were investigated. The response (R-g/R-g) of In-Sn oxides composites to 100 ppm ethanol (C₂H₅OH) was 59.6, which was 7.9 times higher than that of tin oxides at 200℃. The enhanced response to ethanol can be attributed to the change of charge carrier concentration of the nanocomposites and the variation of oxygen adsorption due to the formation of abundant heterojunctions.