Hydration process of magnesia was studied by isothermal calorimetry in the temperature range of 20-40 degrees C. Thereafter, nucleation and growth model was employed to describe the hydration process characterized by hydration heat evolution. Results showed that similar to cement, obvious five stages could be observed in the hydration process of the magnesia at temperature of 20 C. Boundary nucleation and growth model provided a better description of the magnesia hydration process than did the random nucleation and growth model, especially for the sample hydrated at a lower temperature, and the activation energy calculated by kinetics parameters fitted the above models were 57.4 kJ/mol and 53.4 kJ/mol, respectively. In addition, micrographs of magnesia grains before and after hydration were also analyzed, which further indicated the hydration kinetics of the magnesia inclined to the nucleation and growth model. (C) 2012 Elsevier BM. All rights reserved.