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For potential applications in electronic components and sensor elements, lithium-niobium-titanium oxide ceramics are prepared by a solid-state reaction method. Two different weight percentages (2 and 5 %) of ZnO as a functional additive are added before the mechanical milling step in two separate procedures and changes in microstructure, and electrical properties are investigated. Analysis of microstructure by scanning electron microscopy showed the morphology of the synthesized particles in the form of plates and rods, which corresponds to the desired microstructure of the M-phase class of lithium-niobium-titanium oxide ceramic materials. The addition of ZnO creates a trend of increasing the total bulk density. X-ray diffraction analysis by Rietveld refinement and deconvolution of the Raman spectra by Lorentzian line shape fitting enabled the characterization of the crystal structure and vibration properties. In the frequency range from 100 Hz to 10 MHz, the analysis of the obtained impedance spectra at room temperature shows that the tested samples have non-Debye dielectric relaxation. Furthermore, the appearance of one semicircle on the Cole-Cole plots indicates the dominant influence of grain boundary effects on the electrical behavior of the studied ceramics in the measurement frequency range. Finally, a room temperature study of the humidity sensing properties showed that the 2% ZnO sample had a better linear impedance change response over a wide range of relative humidity from 15% to 85% at a frequency of 15 kHz. © 2022 Polish Academy of Sciences. All rights reserved.