Well-dispersed magnesium hydroxide narroplatelets were synthesized by a simple water-in-oil (w/o) microemulsion process, blowing gaseous ammonia (NH3) into microemulsion zones solubilized by magnesium chloride solution (MgCl2). Typical quaternary microemulsions of Triton X-100/cyclohexane/n-hexanol/water were used as space-confining microreactors for the nucleation, growth, and crystallization of magnesium hydroxide narroparticles. The obtained magnesium hydroxide was characterized by field-emission scanning electron microscopy (FESEM), high-resolution transmission election microscopy (HRTEM), X-ray powder diffraction (XRD), laser light scattering, Fourier transform infrared spectroscopy (FT-IR), and thermogravinuetric analysis-differential scanning calorimetry (TGA-DSC). The mole ratio of water to surfactant (omega(0)) played an important role in the sizes of micelles and narroparticles, increasing with the increase of omega(0). The compatibility and dispersibility of narroparticles obtained from reverse micelles were improved in the organic phase. (c) 2008 Elsevier Inc. All rights reserved.