The 2D nanoplates of δ-MnO2 and the 1D nanowires/nanorods of α-MnO2 can be synthesized at room temperature via one-pot oxidation reaction of commercially available divalent manganese compounds. Treating the MnO or MnCO3 precursor with persulfate ions for 1-2 days yields layered δ-MnO2 2D nanoplates, whereas the same oxidation reaction for the MnSO4 precursor produces γ-MnO 2-structured 3D urchins. As the reaction time is extended for ∼14-21 days, not only δ-MnO2 nanoplates but also γ-MnO2 urchins are changed to wellseparated 1D nanostructured α-MnO2 materials with controllable diameters. According to N2 adsorption-desorption isotherm measurements and Mn K-edge X-ray absorption spectroscopy, all the obtained manganate nanostructures show expanded surface areas of ∼50-120 m2 g-1 and the mixed oxidation state of Mn3+/Mn4+, respectively. All the present nanostructured manganese oxides exhibit pseudocapacitance behaviors with large specific capacitance and excellent capacitance retention, highlighting their promising functionality as a supercapacitor electrode. Among the materials under investigation, the δ-MnO2 2D nanoplates show the largest specific capacitance (∼180-210 F g-1). The present finding clearly demonstrates that the room-temperature oxidation reaction of the MnO orMnCO3 precursor can provide a facile soft-chemical route to 2D δ-MnO2 nanoplates and 1D R-MnO2 nanowires/nanorods with highly stable pseudocapacitance behaviors.