In this work, we report a dramatic enhancement in ethanol sensing characteristics of Co-Sn oxides composites with 3D hierarchical architectures, which have been successfully synthesized via an environment friendly one-step hydrothermal approach. The response (resistance ratio) of cobalt oxide and tin oxide composites to 100 ppm ethanol (C₂H₅OH) was 201 at 200℃, representing a significant improvement in comparison to tin oxide 3D hierarchical architectures (7.5, correspondingly). The high response of detection of ethanol can be attributed to the change of charge carrier concentration and the variation of oxygen adsorption due to the formation of abundant heterojunction barriers as well as the tuned catalytic activity of Co components, which induce dissociation of ethanol molecule. The unique nanostructure also played an important role in detecting ethanol gas, due to its contribution in facilitating the transport rate and augmenting the adsorption quantity of the target gas molecules.