In this paper, the dense FexCu0.10Ni0.66Mn2.24−xO4 (0 ≤ x ≤ 0.90) ceramics with accurate stoichiometry are prepared by the route of solid-state coordination reaction. The effect of Fe addition on the electrical properties of the ceramics has been investigated by powder X-ray diffraction (XRD), electrical measurement and thermogravimetric analysis. With Fe content x increasing from 0 to 0.45, the resistivity remains almost unchanged, whereas the thermal constant B decreases drastically. With a further increase in x from 0.45 to 0.90, both the resistivity and the thermal constant B increase. With a rise in x from 0 to 0.9, the aging coefficient drops from 19.9 to 0.6%. The remarkable improvement of the electrical stability can be attributed to the mechanism that substitution of Fe3+ for Mn2+ and Mn3+ restrains the formation of cation vacancies in spinel lattice, thus the modification of cation distribution and the consequent aging under thermal stress is greatly alleviated.