Chemical looping combustion divides combustion into separate reduction and oxidation (redox) reactions that are linked via a particulate oxygen carrier. The resistance of the oxygen carrier to attrition is an important factor that affects its lifetime. Here, we examined the effects of consecutive redox cycles and degrees of reduction on the attrition of ilmenite ore. First, samples were prepared by subjecting ilmenite to 0 to 150 redox cycles in a fluidized-bed reactor. Next, the resistance of the samples to attrition was examined in a laboratory-scale fluidized bed at room temperature. The attrition rate increased with the number of redox cycles, particularly between 50 and 100 redox cycles, and degree of reduction. Observations of the samples via scanning electron microscopy and measurements of their tapped density and reduction rate revealed that the rapid increase was the result of surface morphological changes, including migration of iron toward the particle surfaces. (C) 2019 Elsevier B.V. All rights reserved.