Abstract: We fabricated CuO/ZnO composite nanostructures using an easy one-step hydrothermal method. Samples with different CuO contents were grown by changing the concentration of Cu ions in the reaction solution. The structure and morphology of the samples were tested by scanning electron microscope， X-ray diffraction， and other techniques. We tested the responses of the samples to ethanol gas by an intelligent gas sensing analyzer. The results indicated that the sensitivity of CuO/ZnO composite nanostructures to ethanol gas was significantly enhanced compared with pure ZnO. When the molar ratio of copper ion to zinc ion in the reaction solution was 3 to 5，the gas-sensing performance of the synthesized sample reached the best，and its sensitivity to 100 ×10^-6 ethanol was 55. 3 at the optimum working temperature of 200 ℃. The increased gas sensitivity can be ascribed to the higher specific surface area and p-n junction formation.

Key words: CuO/ZnO composite nanostructure, one-step hydrothermal method, gas sensitivity