facile method is presented to prepare flower-like alpha-Ni(OH)(2) involving only microwave heating of nickel nitrate hydrate in ethanol solvent without any hard/soft templates or precipitate-controlling agents. After calcination procedure, hierarchical and porous NiO nanoflowers with large BET-specific surface areas and controlled pore-size distributions are readily fabricated. A possible formation mechanism is proposed based on self-assembly under microwave heating. The structure, morphology, and crystalline phase of the products are characterized by transmission electron microscopy (TEM), X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and N(2) adsorption/desorption isotherm analysis. TEM reveals that the obtained NiO nanoflowers have uniform size and are composed of sheet-like petals that are built up from nanocrystals. The resultant NiO nanostructures present a specific capacitance as high as 277 F/g and good cycling stability.