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ABSTRACT The cyclic CO2 capture activity of natural CaO-MgO sorbents derived from dolomite or limestone with different MgO contents has been investigated on a TGA, with the consideration of the influence of H2O during the carbonation and calcination. The scanning electron microscopy (SEM) and the brunauer emmett teller (BET) were used to characterize the fresh and used CaO-MgO sorbents. The results have indicated that the natural CaO-MgO sorbent with MgO content of 31.5%-38.7% should be good to improve the cyclic capture activity of CaO. The CaO-MgO sorbent has the best cyclic activity when H2O is present during both carbonation and calcination. H2O changes the sorbent morphology producing bigger particles and pores for the sintering during calcination but makes the sorbent have more stable surface area for the taking palace of the fast kinetic carbonation reaction. Besides, H2O decreases the product layer diffusion resistance and increases the reaction rate during the transition and the product layer diffusion control stage. After sorbent sinters during the reaction cycles, the H2O-improving effect becomes more obvious as the MgO content increases. The results indicate the potential of the natural CaO-MgO sorbent with proper MgO content for cyclic CO2 capture in the presence H2O. Copyright © 2013 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]