Hexagonal magnesium hydroxide (Mg(OH)(2)) nanoflakes were successfully synthesized via hydrothermal method in the presence of the surfactant polyethylene glycol 20,000 (PEG-20,000). Results show that PEG-20,000 plays an important role in the formation of this kind of nanostructure. The composition, morphologies and structure of the Mg(OH)(2) nanoflakes were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The SAED patterns taken from the different positions on a single hexagonal Mg(OH)(2) nanoflake show different crystalline structures. The structure of the nanoflakes are polycrystalline and the probable formation mechanism of Mg(OH)(2) nanoflakes is discussed. Brunauer-Emmett-Teller (BET) analysis were performed to investigate the porous structure and surface area of the as-obtained nanoflakes. (C) 2013 Elsevier Ltd. All rights reserved.