The reduction of CO2 to Carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (MnxFe3-xO4-delta, 0 less-than-or-equal-to x less-than-or-equal-to 1, delta > 0 at 300-degrees-C. They were prepared by reducing Mn(II)-bearing ferrites with H-2 gas at 300-degrees-C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO2 to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mossbauer study of the phase changes of the solid samples during the H2 reduction and CO2 decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, delta, contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO2 to carbon by the donation of an electron at adsorption sites.