A novel room-temperature coordination-precipitation technique was successfully developed for the synthesis of nickel hydroxide (theophrastite) nanoplatelets. This method has great potential for large-scale industrial production owing to facile size-controlled and low-cost. This platelet-like nickel hydroxide precursor can readily be converted to nickel oxide (bunsenite) nanoplatelets after 400 degrees C calcining. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry-differential thermal analysis (TG-DTA) and X-ray photoelectron spectroscopy (XPS) techniques. The thickness of beta-Ni(OH)(2) nanoplatelets can be controlled by changing concentration of precipitant NaOH in the presence of ethylenediamine. The fort-nation of Ni(en)(3)(2+) complex ions in solution prior to precipitating nickel hydroxide may play a crucial role in controlling phase composition of resulting precipitate. (c) 2005 Elsevier B.V. All rights reserved.