© 2022 The Physical Society of the Republic of China (Taiwan)In this study, the solid state reactions under atmospheric conditions were used to create Tb–Gd–Ho co–doped stabilized Bi2O3–based solid electrolyte systems. As the diffraction patterns only included the δ–phase peaks, the XRD results confirmed that all of the samples produced were stabilized in the cubic δ–phase at room temperature. However, a discontinuity indicating a phase transition from monoclinic α–phase to cubic δ–phase occurred at approximately 730°C on the conductivity curve of sample B1 produced by equal dopant percentages of 5% Tb, 5% Gd, and 05% Ho. This sample's DTA curve revealed that no endothermic or exothermic peaks occurred during the heating and cooling cycle, indicating that the phase transition had occurred. In samples produced with dopant content ratios of 1:1:2, 1:2:1, and 2:1:1, the effect of dopant content ratios on electrical conductivity was evidently noticeable. Sample B8 had the highest conductivity of all stabilized samples, with 0.119 S/cm at 750°C, containing 5% Tb, 5% Gd, and 10% Ho dopant percentages, and the lowest activation energy of 0.24 eV.