Hydrogen-activated Ni(II)-bearing ferrite, Ni0.372+Fe0.492+Fe2.093+O4.00, showed a high rate of decomposition of carbon dioxide to carbon at 300 degrees C. This is based on the redox process of the Ni(II)-bearing ferrite with the spinel type of crystal structure. The rates of both activation by hydrogen gas and oxidation in carbon dioxide gas were much improved in the Ni(II)-bearing ferrite. The rate of decomposition was 0.178 mol h(-1) for the activated Ni(II)-bearing ferrite and 0.005 92 mol h(-1) for the activated magnetite in the batch mode, being 30 times larger. The rate of carbon dioxide decomposition was 16 times higher in the flow system in comparison with that of the activated magnetite.