Chemical looping gasification (CLG) is a promising technology to covert solid fuel into synthesis gas efficiently, and oxygen carrier is crucial for CLG. In this work, Co-doped Ca2Fe2O5 brownmillerite oxides were synthesized, and its reactivity as oxygen carriers for microalgae CLG was investigated. The results showed that the Cobalt substitution for Fe improved the activity of oxygen carriers, but excess Cobalt tended to complete oxidation. XPS analysis, thermogravimetric and fixed bed tests indicated that Cobalt doping enhanced the activity of Fe cations in brownmillerite structure, and Ca2Fe1.8Co0.2O5 was proved to be most suitable for microalgae CLG with the highest H-2 yield. In the initial 10 redox cycles, gasification performance with Ca2Fe1.8Co0.2O5 oxygen carrier almost kept stable, and the gasification efficiency and carbon conversion respectively dropped by 3.96% and 2.34%, although impurity phase of spinel oxide and agglomeration was detected. In summary, Ca2Fe1.8Co0.2O5 kept great activity and acceptable stability for synthesis gas production through microalgae CLG. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.