Magnesium hydroxide (Mg(OH)(2)) particles were synthesized and modified via a reaction-hydrothermal process using Ca(OH)(2) and MgCl2 as precursors. The influence of KOH mineralizer on the hydrothermal modification of Mg(OH)(2) was investigated. X-ray diffraction, scanning electron microscopy, thermogravimetry and specific surface area analyses indicated that KOH played a key role in the recrystallization of Mg(OH)(2). It was found that the morphology and dispersion of Mg(OH)(2) particles improved significantly with an increase of KOH concentration from 1 to 4 mol/l. (c) 2009 Elsevier B.V. All rights reserved.