Spray pyrolysis is a favorable technique to form complex mixed-metal oxide powders with high purity in high temperature region. Manganese oxide powders were prepared by spray pyrolysis from an aqueous solution of $Mn(NO_3)_2$. Powders were formed in the temperature range of 500~$700^{circ}C$ under the constant pressure of 300torr. All the powders have hydrous forms. When the temperature was increased, the size and the surface area of the particles decreased. An electrochemical capacitors were made with manganese oxide electrodes and KOH electrolyte. With the temperature decreased, capacitors showed high capacitance. Capacitor which was prepared with powders formed in the temperature $500^{circ}C$ demonstrated specific capacitances as high as 83F/g.