Increasing and constant temperature gravimetric methods were used to measure the thermal decomposition rates of Mg(OH)2 particles. An Arrhenius-type kinetic equation was proposed and tested. Temperature, exposure time on surface area of the calcined particles and other effects of variables were explored. A fractional-order sintering rate expression was developed on the basis of collected experimental data. An integrated model is also presented that considers the surface area generation by calcination and the simultaneous surface reduction caused by sintering of the nascent oxide. Obtained results enable specifying the operating conditions needed for the production of the high surface, reactive magnesium oxide.