The study of 7YSZ (93% ZrO 2-7% Y 2 O 3), 8YSZ (92% ZrO 2-8% Y 2 O 3), and CSZ (88% ZrO 2-12% CaO) as SOFC electrolytes have been carried out successfully. 7YSZ and 8YSZ powders were prepared by solid state reaction method of mixed Y 2 O 3 and ZrO 2 followed by calcination at 1350 C for 1 hour, while CSZ was commercial products. Pellets of 7YSZ, 8YSZ, and CSZ were prepared by 1.2 gr, pressed at 40 MPa and sintered at 1550 C for 4 hours. Rietveld refinement revealed that 7YSZ comprised 47.27% monoclinic, 52.65% cubic, and 0.008% Y 2 O 3 cubic, while 8YSZ comprised 48.45% monoclinic, 49.32% cubic, 2.23% Y2O3 cubic and CSZ has 88% ZrO 2 and 12% CaO. Ionic conductivity and activation energy were obtained from Cole-Cole Plot of impedance, the activation energy of 7YSZ= 1.03 eV, 8YSZ= 0.96 eV and CSZ= 0.78 eV.