In this context, and to isolate the specific influence of Fe oxidation state, this work explores the synthesis, characterization, and catalytic performance of highly oxidized barium-iron perovskites, obtained by both high and low temperature oxidation treatments, starting from the 6H-BaFeO2.78 phase. To this end, oxides with compositions BaFeO2.96 (0.92 Fe IV : 0.08 Fe III /unit formula) and BaFeO2.90 (0.80 Fe IV : 0.20 Fe III /unit formula) have been prepared and characterized to completely assess their oxygen content and microstructural features, using a variety of diffractometric and electron microscopy techniques. In parallel, an in-depth characterization of the BaFeO3-δ redox properties was performed through in-situ High Temperature-Neutron Diffraction (HT-ND), Selected Area Electron Diffraction (SAED) and High Resolution Transmission Electron Microscopy (HRTEM). The influence of oxygen stoichiometry on catalytic CO oxidation activity has been also assessed.