(Bi2O3)(1-x-y)(Dy2O3)(x)(Tm2O3)(y)ternary systems as electrolytes were synthesized at 750 degrees C by the solid-state ceramic synthesis method. Eight (Bi2O3)(1-x-y)(Dy2O3)(x)(Tm2O3)(y)(x= 0.1, 0.2) and (y= 0.05, 0.1, 0.15, 0.2) electrolytes at different ratios were investigated. The structural, electrical, and thermal properties of these eight electrolytes for solid oxide fuel cells (SOFCs) were characterized by means of a X-ray powder diffractometer (XRD), the four point-probe technique (4PPT), and thermal gravimetry/differential thermal analysis (TG/DTA). Results of XRD measurements showed that the delta-Bi2O3(cubic) phase with a stable structure was dominantly obtained for all of the samples. As a result of the temperature-dependent electrical measurements of these ternary systems, it was found that electrical conductivity decreases with increasing molar ratio of Tm2O3. The highest electrical conductivity was found for the sample of the (Bi2O3)(0.85)(Dy2O3)(0.10)(Tm2O3)(0.05)system as 0.349 (omega cm)(-1)at 750 degrees C. The lowest activation energy was found for the same sample as 0.68 eV.