Zn1-xNixO thin films (x = 0, 0.05, 0.10, 0.15 and 0.20) were systematically synthesized by Successive Ionic Layer Adsorption And Reaction (SILAR) method with 40 SILAR cycle and then were annealed at 300 degrees C. Influence of nickel doping and annealing treatment on the structural, morphological, optical and gas sensing properties of Zn1-xNixO thin films were investigated. X-ray diffraction (XRD), scanning electron microscope (SEM) and optical absorption measurements were used for characterization of the films. The gas sensing properties of the Zn1-xNixO sensors for low nitric oxide (NO) gas concentrations were investigated as a function of operating temperature and doping concentration. The gas sensing results showed that the doping process strongly influenced the response of ZnO sensors. The optimal operating temperature of the sensors was found of 95 degrees C, the response of the annealed Zn0(0.90)Ni(0.10)O sensor for 25 ppm NO reached a maximum of 63%. The Zn0.90Ni0.10O sensor exhibited higher response and better response/recovery times than the others. It was concluded that Ni doping and annealing treatment enhanced the gas sensing properties of sensors by changing microstructure, morphology, bandgap of ZnO films.