Proton-conducting ceramic oxides working in the temperature range from 500°C to 900°C may be applied in solid oxide fuel cells (SOFC), electrolysis cells, H₂ separators, gas sensors and other devices. In this work the first results of the studies of magnesium-doped La_0.98Mg_0.02NbO₄ electrolyte materials are presented. The structure, microstructure and electrical properties of the samples synthesized with the conventional solid-state method (SS) and the composite samples obtained with the TGG method are compared. The microstructure and electrical properties of the studied materials depended strongly on the synthesis method. The composite samples showed partial crystallographic orientation. It was proposed that owing to this, the conductivity of the composite samples was comparable or larger than that of other doped ortho-niobates.