Magnesium hydroxide (Mg(OH)(2)) is widely used in different applications, including as a magnesium oxide precursor. Therefore, understanding the different physicochemical properties as a function of pressure is important. In this work, a systematic thermal analysis was performed at high pressure using differential scanning calorimetry. The dehydroxylation enthalpy (Delta H) of Mg(OH)(2) was determined at different pressures. The results showed that between atmospheric pressure and a pressure of 500 psi, Delta H increases due to a reaction equilibrium shift. However, at pressures higher than 500 psi, Delta H decreases significantly. At these high pressures, the reaction occurs at temperatures above the critical temperature, resulting in the production of overheated steam. (C) 2011 Elsevier B.V. All rights reserved.