Nanostructured transparent and conductive p-type NiO thin films were prepared successfully by RF sputtering from a Ni metal target [1, 2]. The effect of thickness on the structural and optical properties of NiO nanocrystalline thin films was studied. Ultraviolet–visible (UV–Vis), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to characterize the NiO nanocrystalline thin films. The AFM studies showed that the roughness parameters of the NiO surfaces are affected by the film thickness. The grain size increased with increasing film thickness. The XRD analysis of the NiO thin layers revealed a high crystalline structure with a preferred crystalline orientation in the (002) plane. The optical transparency of the NiO layers for T > 100°C exceeds 80% throughout the interval of the visible spectrum. The free carrier concentration reached the value of 2.12 ´ 1016 cm–3 at a substrate temperature of 300°C. An increase in the substrate temperature from 50 to 450°C leads to a decrease in the resistivity of the NiO layers due to an increase of the concentration and mobility of the free carriers. The increase in the carrier concentration is attributed to the formation of some acceptor centers (oxygen vacancies) with an increase in the substrate temperature. An increase in the free carrier concentration leads to a significant increase in the difference in the band gap values due to the Burstein–Moss effect. The increase in the Hall mobility correlates with the results of the structural studies, which show that the crystallite size increases with an increase in the substrate temperature.