Mn(II)-ferrite (Mn0.97Fe2.0204.00) prepared by the wet method was reduced in a hydrogen at 300 C to form highly reactive mangano-wustite ((Fe0.67, Mn0.32) 0) for CO2 decomposition. Approximately 23% CO2 injected (3.40 mmol) was decomposed to CO by the mangano-wustite (3.22 g) in the initial stage of the reaction in a batch system at 400-degrees-C. 88% CO was further decomposed to carbon. Approximately 58% CO2 injected was reversibly adsorbed on the surface and the remaining 12% was unchanged after 200 h reaction. The mangano-wustite was concurrently transformed to Mn(II)-bearing ferrite (Mn0.23Fe2.7704.00) and manganese-rich mangano-wustite ((Fe0.60, Mn0.40)O). The higher CO2 decomposition capacity for this mangano-wustite than that for oxygen-deficient Mn(II)-ferrite is discussed in detail, based on electron hopping and movement of ions in the bulk.