Nano-sized and well dispersed manganese oxide and nickel-manganese oxide (Ni-Mn-O) powders are synthesized via the hydrothermal route. The addition of nickel ions significantly affects the morphology, particle size and the electrochemical properties of the obtained powders. Adding nickel ions results in a significant change in the shape of the powders from rod-like to plate-like. The electrochemical analysis of the electrode reveals that the specific capacitance of the synthesized powders is greatly increased with the addition of nickel ions. When the hydrothermal temperature is increased to 125 degrees C, the specific capacitance also increases to 284 F/g and decreases by about 4% after 1500 cycles of charge and recharge. Ni-Mn-O is considered to be a promising material for the electrodes used in electrochemical capacitors. (c) 2012 Elsevier B.V. All rights reserved.