The NiO films were deposited by RF reactive magnetron sputtering from a Ni target in a mixture of oxygen and argon gases onto heated Si and Coming 7059 glass substrates. The influences of process parameters including RF power, O-2/Ar ratio, and substrate temperature on the film properties such as O/Ni atomic ratio, crystallographic structure, preferred orientation, transmittance and resistivity were then investigated. The results show that deposition rate is an approximately linear function of RF power. Only the (200) diffraction peak is found in the XRD patterns of the deposited NiO films. The values of O/Ni atomic ratio in the thin films are between 1.87 and 1.80. It decreases as the substrate temperature is increased. The transmittances of undoped NiO films show a strong dependence on the O-2/Ar ratio. With increasing O-2/Ar ratio, the transmittance decays. The film resistivity increases with increased substrate temperature. The conduction in nickel oxide is due to the presence of Ni+3 ions, which are formed due to nickel vacancies in the films.