Pure hexagonally layered alpha-Co(OH)(2) powder is prepared in large quantity by precipitation method under mild conditions. Subsequently, anion-exchange reaction and aging treatment in alkaline medium are performed to find their influence on the microstructure and supercapacitive properties of alpha-Co(OH)(2). Various inorganic anions are successfully intercalated into the interlayer gallery of alpha-Co(OH)(2) with the morphology and structure reserved. While the alpha-Co(OH)(2) transforms into other cobalt compounds by aging treatment 1 Mol L-1 KOH solution at room temperature. The effects of anion-exchange on the supercapacitive properties are evaluated by cyclic voltammetry and galvanostatic charge-discharge tests. The alpha-Co(OH)(2) exhibits a high specific capacitance, good rate capability and improved stability after intercalation with nitrate and sulfate. The morphology and structure of alpha-Co(OH)(2) after 2000 continuous charge-discharge tests in 1 Mol L-1 KOH electrolyte are also well maintained, indicating its excellent stability in charge-discharge tests. In contrary, the phase transitions from alpha-Co(OH)(2) to beta-form and other cobalt phases lead to a dramatic decrease in the specific capacitance, from 763.4 F g(-1) to 25.9 F g(-1) (C) 2014 Elsevier B.V. All rights reserved.