The O-2/CO2 coal combustion technology is an innovative combustion technology that can control CO2, SO2 and NOx emissions simultaneously. Calcination and sintering characteristics of limestone under O-2/CO2 atmosphere were investigated in this paper. The pore size, the specific pore volume and the specific surface area of CaO calcined were measured by N-2 adsorption method. The grain size of CaO calcined was determined by XRD analysis. The specific pore volume and the specific surface area of CaO calcined in O-2/CO2 atmosphere are less than that of CaO calcined in air at the same temperature. And the pore diameter of CaO calcined in O-2/CO2 atmosphere is larger than that in air. The specific pore volume and the specific surface area of CaO calcined in O-2/CO2 atmosphere increase initially with temperature, and then decline as temperature exceeds 1000 degrees C. The peaks of the specific pore volume and the specific surface area appear at 1000 degrees C. The specific surface area decreases with increase in the grain size of CaO calcined. The correlations of the gain size with the specific surface area and the specific pore volume can be expressed as L = 744.67+464.64 1g(1/S) and L = -608.5+1342.42 1g(1/epsilon), respectively. Sintering has influence on the pore structure of CaO calcined by means of influencing the gain size of CaO. (C) 2006 Elsevier B.V. All rights reserved.