Various polymorphs of MnO2 were synthesized under a controlled hydrothermal method. The structure characteristics and ion exchangeability were studied by XRD, TEM, Li+ adsorption isotherm, kinetics and selectivity measurement. The MnO2 nanowires, mainly about 5 x 400nm in diameter and length, are found to have a remarkable lithium ion-sieve property with equilibrium distribution coefficients (K-d) in the order of Na+ < K+ < Mg2+ < Ca2+ << Li+, Li+ monolayer saturation amount of 2.43 mmol g(-1), and the first-order adsorption rate constant of 2.16 x 10(-6) s(-1), which is promising in the lithium extraction from brine or seawater. (c) 2007 Elsevier Ltd. All rights reserved.