We report the nature of rare earth ion doped ceria (REC), Ce0.8Ln0.2O2−δ, (Ln = Y 3+ , Gd 3+ , Sm 3+ , Nd 3+ and La 3+ ) as oxide ion conductors for their plausible application as electrolytes in intermediate temperature solid oxide fuel cell (SOFC). The samples were prepared by citrate-complexation method and characterized by XRD, SEM/ EDX and UV-Visible spectra. The cubic fluorite-type crystal structure is confirmed from XRD patterns, and the observed lattice parameters are in agreement with calculated values. The UV-Vis spectra of the particles dispersed in aqueous medium showed absorption in the UV region which is ascribed to charge-transfer transition. The dc conductivities at 673 K are in the order of Ce0.8Sm0.2O2−δ > Ce0.8Gd0.2O2−δ > Ce0.8Y0.2O2−δ > Ce0.8Nd0.2O2−δ > Ce0.8La0.2O2−δ and their corresponding activation energies are 0.85, 0.87, 0.87, 0.88 and 0.95 eV. Based on ionic and electronic transference numbers, electrical conductivity obtained here is purely ionic, i.e., oxide ion conductors.