In this work, La0.85Sr0.15–xBaxGa0.85Mg0.15O3–δ (LSBGM), with 0 ≤ x ≤ 0.075, were prepared as electrolytes for solid oxide fuel cells applications. The effect of barium and sintering temperature on the structure and electrical properties was studied. A fast combustion method was used, starting with nitrate salts and citric acid as fuel. The XRD spectra showed two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM-cubic (space group Pm-3 m). From literature, both structures are reported as high oxygen ion conductive species, but normally, they are not reported to appear together. Major secondary phases were LaSrGaO4, BaLaGaO4, and BaLaGaO7. SEM revealed a material with low porosity, indicating incomplete densification. The sample La0.85Sr0.075Ba0.075Ga0.85Mg0.15O3–δ showed a conductivity of 0.016 and 0.058 S cm−1 at 600 °C and 800 °C, respectively. This means an improvement of 34% compared to the non-barium sample La0.85Sr0.15Ga0.85Mg0.15O3-δ at 600 °C. Thus, this composition could be used in SOFC. Graphical abstract: [Figure not available: see fulltext.].