Al2O3 nanoparticles were prepared by reverse microemulsion method that uses cyclohexane, polyethylene glycol octylphenyl ether (TritonX-100), n-butylalcohol, and water. The structure, morphology, and specific surface area of the nano-alumina particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), and specific surface area analysis. The specific surface area of the nano-alumina particles was about 450 m2·g-1 (changing with different reaction parameters) and the crystal structure was γ-Al2O3. The particle size was smaller than 10 nm and very uniform. The effect of molar ratio of water to surfactant (r0), volume ratio of surfactant to assistant-surfactant (φ), and calcination temperature (T) on the characteristics of the product were studied. The results indicated that the nano Al2O3 powder with a high specific surface area, high pore volume, od dispersibility, and narrow particle size distribution was obtained at r0=20, φ=0.5, and T=500 ℃.