NiO thin films were grown directly on the Al₂O₃substrates by electrochemical deposition. The H₂S gas sensing properties of the thin films were enhanced by Cu doping. The X-ray diffraction revealed the as-prepared films were NiO crystalline phase. The scanning electron microscope showed the film has 1.87 μm thickness and pores of different sizes, more porous has a higher exposed surface, which can provide more active sites for reaction with the gas. The atomic force microscopy characterization further confirmed the high roughness and porosity of the thin films. Gas sensitivity test displayed that the thin film sensor based on Ni: Cu molar ratio of 9:1 exhibited the highest response and good selectivity to H₂S at 140 °C. Furthermore, the NiO doped by Cu thin film gas sensor also possesses good stability and low detection limit of 100 ppb. The extraordinary gas sensing properties can be attributed to the lamellar structures with the porous channel and substitution doping of Cu.