A ceramic composite with a mixed conducting oxide that has perovskite type crystal structure of {Ln1−aAa}{BxB′yB″z}O(3−δ) where a, x, y, and z are within the range of 0.8≦a≦1, 0<x, 0<y≦0.5, 0≦z≦0.2, 0.98≦x+y+z≦1.02, and δ denotes a value that is determined so as to meet a charge neutralization condition. A denotes a combination of one or more kinds of elements selected out of Ba, Sr, and Ca. B denotes a combination of one or more kinds of elements selected out of Co, Fe, Cr, and Ga, the combination always containing Fe or Co. B′ denotes a combination of one or more kinds of elements selected out of Nb, Ta, Ti, and Zr, the combination always containing Nb or Ta. The present invention is also directed to a mixed conducting oxide and a ceramic composite. The mixed conducting oxide is of formula AFexO(3−δ). A is selected out of Ba, Sr, and Ca, and is within the range of 0.98≦x≦1.02, and δ denotes a value determined so as to meet the charge neutralization conditions.