The objective of this study was to establish the reaction kinetics involved in redox cycles of the CaMn0.9Mg0.1O3-delta material to be used as an oxygen carrier in the chemical-looping-combustion process. The oxygen-transport capacity and reactivity of this material during consecutive reduction and oxidation steps with gaseous compounds (CH4, H-2, CO, and O-2) were studied in a thermogravimetric analysis apparatus. The oxygen uncoupling properties of this material were also analyzed. It was found that material reactivity increased with the number of redox cycles, whereas the oxygen-transport capacity decreased with the cycle number until it was stabilized or "activated". Conversion versus time curves at different temperatures (973-1273 K) and reacting gas concentrations (5-60 vol %) were used for kinetic determination. The grain model with control by chemical reaction and diffusion through the product layer was used to obtain the kinetic parameters for fresh and "activated" particles.