Sol–gel method has been employed for the synthesis of nanocrystalline nickel oxide (NiO). The NiO powders were sintered at 400–700 °C for 1 h in an air. Thin films of sintered powders were prepared on glass substrate using spin coating technique and changes in the structural, morphological, electrical and optical properties were studied. The structural and microstructural properties of nickel oxide films were studied by means of X-ray diffraction and field emission scanning electron microscopy. Structural analysis shows that all the films are crystallized in the cubic phase and present a random orientation. Surface morphology of the nickel oxide film consists of nanocrystalline grains with uniform coverage of the substrate surface with randomly oriented morphology. The electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 10⁻⁴ to 10⁻² (Ω cm) ⁻¹ after sintering. The electron carrier concentration (n) and mobility (μ) of NiO films annealed at 400–700 °C were estimated to be of the order of 1.30 to 3.75×10¹⁹ cm⁻³ and 1.98 to 4.20×10⁻⁵ cm2 V⁻¹ s⁻¹. The decrease in the band gap energy from 3.86 to 3.47 eV was observed for NiO sintered between 400 and 700 °C. These mean that the optical quality of NiO films is improved by sintering.