CuO-ZnO p-n junction nanowires were synthesized by a simple two-steps route for ethanol sensing application. Display omitted •Nanosized p-n junctions of CuO nanoparticles and ZnO nanowires were constructed.•CuO nanoparticles and ZnO nanowires were well-crystallized with the average diameter of around 30 nm.•Gas sensors based on CuO-ZnO p-n junction nanowires were fabricated and their gas sensing properties were compared.•Ethanol sensing performance of pure ZnO nanowires were effectively improved by the p-n junction construction. CuO-ZnO p-n junctions were constructed by precipitating CuO nanoparticles on the surface of ZnO nanowires followed by an annealing process. The molar ratio of Cu to Zn in the final composites was controlled by regulating Cu content in the precursor solution. XRD, SEM, TEM, EDS, and XPS were used for the structural characterization of the prepared samples. The results confirmed that the monoclinic CuO nanoparticles were closely and uniformly attached on the surface of the hexagonal ZnO nanowires to form the p-n junctions. Notably, the one-dimensional structure of the host ZnO nanowires was well-maintained during the p-n junction construction process. Five sensors based on CuO-ZnO p-n junction nanowires with different Cu/Zn ratios as well as the pure ZnO nanowires were fabricated and their gas sensing performance was systematically compared. The formation of CuO-ZnO p-n junction effectively enhanced the ethanol sensing properties of the host pure ZnO nanowires. And 5%CuO-ZnO exhibited the highest ethanol response at the operating temperature of 300 °C, which was about 4 times higher than that of the pure ZnO. Several factors and considerations were then discussed for the explanation of the distinct sensing behaviors of these sensors.