Self-reassembled MnO2 nanosheets were prepared via nanosheet processes and their electrochemical properties were investigated in 0.1 M Na2SO4 aqueous solution. The MnO2 nanosheets had a plate-like morphology: 2 mu m in width and 2 nm in thickness. The electrochemical properties of the MnO2 nanosheet electrodes were largely influenced by the particle size, and a MnO2 nanosheet electrode composed of small-sized particles (fine-NS-MnO2) exhibited a relatively large discharge capacity of 182 F/g-MnO2 compared with the conventional MnO2 electrode capacity of 153 F/g-MnO2 at a current density of 100 mA/g-MnO2. The fine-NS-MnO2 had a large mesoporous volume and large specific surface area, and thus exhibited a good rate capability. In contrast, the MnO2 nanosheet electrode composed of large-sized particles (NS-MnO2) showed poor rate capability due to the large ionic diffusion resistance. Microstructural control by nanosheet processes and reduction of the particle size are important for the design of MnO2 electrodes with superior electrochemical properties. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.028209jes] All rights reserved.