Chemical looping combustion (CLC) presents a new method to increase the utilization efficiency of biomass. Due to the existence of ash in biomass, the interaction between biomass ash and oxygen carrier is a significant concern during the biomass CLC process. Three typical biomass ashes were added into an iron ore oxygen carrier, and their effects on the performance of oxygen carrier were carried out during the CLC process. The effects of some key variables on the performance of oxygen carrier were evaluated, including biomass ash type, ash addition ratio (0-20%) and cycle number. The results indicate that fuel conversion was significantly influenced by the addition of biomass ash. The addition of SiO2-rich wheat straw ash (WSA) was likely to be converted into potassium silicates, and it caused serious particle sintering of oxygen carrier. It led to a reactivity decrease of oxygen carrier and its reduction extent was slighter. In contrast, fuel conversion was always promoted by the addition of corn stalk ash (CSA) and rape stalk ash (RSA), i.e., K2O-rich ashes with a relatively lower SiO2 content. A slight reactivity decrease was also observed at a high CSA ratio (20%). Cycle experiments indicate that the iron ore activated by CSA and RSA has a relatively stable reactivity promotion. Finally, possible mechanisms for the enhanced performance of iron ore by biomass ash were explored. (C) 2015 Elsevier B.V. All rights reserved.