Hydrophobicity magnesium hydroxide nanoneedles were synthesized via direct precipitation method by using stearic acid as surfactant, magnesium chloride hexahydrate in the presence of acetone as precursor and industrial ammonia as precipitator in this paper. The morphology, crystal phase was observed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) while the thermal gravity analysis (TGA) technique was used to analyze the thermal behavior of the superfine magnesium hydroxide. The experiment results showed that the hydrophobicity of products was significantly improved and the particles with regular circular-shaped were completely turned into needle-like particles with increasing the use level of stearic acid. (C) 2008 Elsevier B.V. All rights reserved.