Non-stoichiometric niobium nitride films of various nitrogen compositions were deposited on glass and silicon (111) substrates, heated to 150 C, by direct current reactive magnetron sputtering from a niobium metal target in an argon-nitrogen atmosphere. The argon gas flow was fixed at 20 seem and the nitrogen gas flow was changed from 0 to 8 seem. Composition, structure, electrical and optical properties of the films were studied using respectively, energy dispersion spectroscopy, X-ray diffraction, four probes method and optical spectrometry. Thickness was measured by X-ray reflectometry. The structures found were hexagonal for the 2 seem sample and of NaCl type for 4 seem samples and beyond. The film thickness indicates that the deposition rate decreases as the nitrogen gas flow increases. Electrical resistivity increases with the nitrogen content for samples having NaCl structures. Moreover, optical spectrometry shows that samples with NaCl structure have a high reflectivity in infrared region while reflectivity remains low in the ultraviolet region. (C) 2003 Elsevier Science B.V. All rights reserved.