Superfine magnesium hydroxide with monodispersity was synthesized via direct precipitation method in this paper. The particle size and its distribution, morphology, crystal phase, and thermal behavior of the samples were characterized through ultrasonic particle size analyzer (UPSA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry (TG), respectively. The UPSA analysis and TEM observation showed that regular-shaped and monodisperse particles with a smaller particle size ((d) over bar = 314nm) were obtained. The experimental data also confirmed that the synthesized product possessed high purity and its crystal structure was very perfect. (C) 2007 Elsevier B.V. All rights reserved.