In this paper we present the results concerning the characterisation of nickel oxide thin films deposited by d.c. reactive magnetron sputtering. Different NiO thin films have been prepared by changing some deposition parameters, as the oxygen content in the reactive plasma and the sputtering mode (metal- or oxide-sputtering mode). The structure and surface morphology of the samples have been analysed by XRD and by atomic force microscopy and scanning electron microscope, respectively. The electrical responses of the NiO films towards NO, have been also considered. NiO thin films showed good responses to low NO, concentrations (1-10 ppm) with a maximum at 160 degreesC operating temperature.