This paper addresses the grain characteristics and growth model of nano CaO under high-temperature calcination conditions. Nano CaO samples derived from nano CaCO(3) were prepared with a chamber calciner under different calcination times (10-480 min) and temperatures (750-900 degrees C) to study the nano CaO grain growth. X-ray diffractometer and the Scherrer formula were used to test and calculate the grain size of nano CaO. The microstructure and sorption performances of nano CaO were observed by a nitrogen adsorption/desorption apparatus and a thermogravimetric analysis. The results showed that the grain size of CaO grew faster as the calcination temperature increased. A growth asymptote was approached by prolonging the consecutive calcination time. A grain growth model for nano CaO was built according to solid phase sintering theory for the following conditions: 10-120 min isothermal calcination at 750-900 degrees C. The activation energy for nano CaO grain growth was calculated as 120 kJ/mol. In addition, the relation of grain growth, structural properties and CO(2) adsorption performance of nano CaO are discussed. (C) 2011 Elsevier B.V. All rights reserved.