The influence of CaCl2 on the hydrothermal modification of Mg(OH)(2) was investigated in this paper. The experimental results indicated that dispersive Mg(OH)(2) hexagonal plates with the regular shape, the enlarged size and the perfect crystallinity were formed by treating the irregular Mg(OH)(2) agglomerates at elevated temperatures in dilute CaCl2 solutions. Thermodynamic analysis showed that the presence of CaCl2 at the elevated temperature promoted the formation of MgOH+, which was favorable for the formation of Mg(OH)(6-)(4) and the growth of Mg(OH)(2) crystals. (c) 2006 Elsevier B.V. All rights reserved.