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Electrical conductivity studies of alkaline earth oxides doped ceria Ce 0.9 M 0.1 O 2-δ , (where M=Ca and Mg) is reported in this work. The samples were prepared at room temperature by mechanical milling. X-ray diffraction patterns confirm the cubic fluorite structure. Scanning electron micrographs of MgO doped sample shows the presence of the segregation of Mg 2+ which results a negative effect on the electric properties of the MgO doped sample. Frequency dependence of ac conductivity (σ ac ) of these oxide ion conductors showed a remarkably different behavior from that of the cation ones. As temperature increases above 350°C, ac conductivity σ ac in the low frequency range was strongly influenced by space charge polarization at grain boundary and the high frequency plateau agreed with the bulk conductivity of the system. Bulk and grain boundary conductivity studies show that CaO doped ceria exhibit better electrical properties compared to MgO doped sample.