The high-dispersed lamellar ultrafine magnesium hydroxide was obtained at relatively low hydrothermal temperature in the presence of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). The procedure described in this study is attractive since proper amount of CTAB could promote the dissolution and precipitation of magnesium hydroxide in hydrothermal system, resulting in the well-defined morphology, narrow size distribution and good crystallinity of ultrafine particles. The resultant magnesium hydroxide was characterized by X-ray powder diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), field-emission scanning electron microscopy (IFESEM) and laser diffusion analysis. The method led to the production of particles with mean size of 400 nm and a thickness of 60 nm. The optimal conditions of preparation were hydrothermal treatment at 150 degrees C for 6 h at pH 11 with Mg2+/CTAB molar ratio of 80. (C) 2008 Elsevier B.V. All rights reserved.