In the present paper, NiO thin films were prepared on glass substrates using a spin coating method with 0.7 M. There the NiO thin films were heated at different crystallization temperatures of 25, 450, 500, 550 and 600 °C for 2 hours. XRD spectra of prepared NiO thin films indicate that the films have a polycrystalline structure; it is the cubic type of NiO. We have obtained that the crystallite size was increased to the maximum value of 50.32 nm of (200) plane was obtained at 600 °C. We conclude that the crystallinity of NiO thin films was improved with increasing crystallization temperature, it depends too few defects. Spectrophotometer (UV-vis) of NiO films shows an average optical transmission of about 85%. The optical bandgap energy was increased after crystallized from 3.101 for without crystallization to 3.855 eV for a crystallized film at 500 °C. At high crystallization temperature, we found that the NiO thin films have the lowest disorder, the minimum Urbach energy was obtained at a temperature of 600 °C is 180 meV. The NiO thin films have a good electrical property with the minimum of the sheet resistance was found at a lower temperature.