In this research, pure nickel oxide (NiO) nano-thin films were prepared by sol-gel technique using dip deposition method on glass substrates at 100°C. The structural properties of all prepared thin films were studied using X-ray diffraction (XRD) technique, while the optical properties of the prepared films were studied using UV-Vis spectroscopy. The XRD results showed that the nickel oxide films have a cubic polycrystalline structure and that the predominant crystallization direction is (111). The interplaner distance for all peaks and the lattice constants were calculated, and these values were found to be in agreement with the International Standards Card for NiO. The crystallite size of the films prepared at 100°C was 23.97 nm, and the dislocations and number of crystals per unit area were also calculated. The optical properties of the prepared films were studied by recording the transmittance and absorbance spectra over the wavelength range (300-800) nm. The optical properties results showed that the light transmittance of the films increases with increasing wavelength by (>90%) in the visible light region and near the infrared region, and the absorbance decreases with increasing wavelength and that the absorption edge is located at 360 nm with an absorption energy of about (3.44 eV). The results obtained from the (NiO) films indicate that it is a semiconductor with a wide optical energy gap of (3.61eV)................. Key words:...... Nanomaterials, Semiconductor, Optical properties, Structure properties, Sol-gel.