Iron atoms are present in a 3.56 average oxidation state (0.56 Fe IV : 0.44 Fe III / unit formula). Concerning its catalytic performance, our results showed that BaFeO2.78 displays higher catalytic activity than other lanthanide-containing ferrites with a T50% value between 50 and 80 K lower. Temperature-programmed reduction under H2 and CO evidenced the involvement of lattice oxygen in CO oxidation, even at low temperatures (ca. 500 K). The removal of lattice oxygen by hydrogen pretreatment significantly decreased the catalytic activity and increased the light-off temperature, thus supporting the involvement of labile oxygen species as well as the occurrence of an intrafacial reaction mechanism.