Ceria based electrolyte materials are very useful in intermediate-temperature solid oxide fuel cell (IT-SOFC). The compositions Ce_0.85Gd_{0.15 - x}Ca_xO_{2 - δ} (x = 0.0 - 0.075) were prepared through sol-gel method. Their structure was studied by X-ray diffraction. Dense ceramic Ce_0.85Gd_{0.15 - x}Ca_xO_{2 - δ} samples were prepared by sintering the pellets at 1300°C. The lattice parameter was calculated by Rietveld refinement of XRD patterns. Four probe A.C. impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria ceramics in the temperature range 200°C - 700°C. The Ce_0.85Gd_{0.15 -x}Ca_xO_{2 -δ} composition showed maximum ionic conductivity with less activation energy.