Highly uniform gamma-MnO2 3D urchinlike and sisallike nanostructures have been successfully prepared by a common hydrothermal method based on the reaction between MnSO4 and KBrO3. Reaction temperature and the additives of the polymers play an important role in influencing the morphologies of the as-obtained products. These urchinlike and sisallike nanostructures, which own the highly specific area on the surface of the particles may provide more possibility to give an ideal host material for the insertion and extraction of lithium ions, to realize region-dependent surface reactivity, and to act as molecular sieves.