Non-stoichiometric Ni1-xO thin films were prepared on glass substrate by direct current reactive magnetron sputtering in a large range of oxygen partial pressure (0 <= p(02) <= 1 Pa). The dependence of the deposited film structure and properties on oxygen stoichiometry were systematically analyzed by X-ray diffraction, X-ray reflectivity, X-ray photoemission spectroscopy, Raman spectroscopy, atomic force microscopy, UV-vis measurements and electrical transport properties measurements. The deposition rates, surface morphology and opto-electrical properties are very sensitive to the oxygen partial pressure lower than 0.05 Pa due to the presence of metallic nickel cluster phase determined by X-ray diffraction, X-ray reflectivity and XPS spectroscopy. Presence of nanocrystallized NiO phase was highlighted even for P-02 = 0 Pa. For p(02) > 0.05 Pa, only the NiO phase was detected. Progressive appearance of Ni3+ species is characterized by a fine increase of the lattice parameter and (111) preferred orientation determined by grazing angle X-ray diffraction, fine increase of the X-ray reflectivity critical angle, displacement of the Ni 2p(3/2) signal towards lower energy, significant increase of the electrical conductivity and decrease of the total transmittance. Quantification of Ni3+ by XPS method is discussed. We also showed that the use of Raman spectroscopy was relevant for demonstrating the presence of Ni3+ in the Ni1-xO thin films. (C) 2017 Elsevier B.V. All rights reserved.