Two-step calcination (CO2 and N-2 atmospheres) was used to modify the microstructure of natural dolomite for high-temperature CO2 capture. Two other one-step calcinations (CO2 or N-2 atmosphere) were provided for comparison. Different morphological characterizations (thermal decomposition, phase composition, morphology, and nitrogen adsorption) were performed, followed by an analysis of 30 carbonation/calcination cycles in a fixed bed reactor. During primary calcination in a CO2 atmosphere, an intermediate phase (MgxCa(1-x)CO(3)) was observed by TG and XRD results, which hindered the de-mixing of CaO and MgO in the secondary calcination in a N-2 atmosphere. Therefore, two-step calcination produced smaller grains (CaO: 45.2 nm; MgO: 32.6 nm), larger specific surface area (21.08 m(2)/g) and pore volume (0.082 cm(3)/g) and uniform distribution of CaO and MgO, which resulted in a higher and more stable uptake of CO2 compared to the results from one-step calcinations. (C) 2015 Elsevier B.V. All rights reserved.