Manganese oxide nanotubes are electrochemically synthesized by the cyclic voltammetric electrodeposition method. A transmission electron microscopy investigation shows that these nanotubes are MnO2 crystalline with a diameter of 20 nm. Field-emission characteristics of the synthesized manganese oxide nanotubes are measured. The turn-on field is about 8.4 V/mum at a current density of 1 muA/cm(2). The emission current density and the electric field follow Fowler-Nordheim behavior. Therefore, these manganese oxide nanotubes are useful for field-emission applications because they can be easily and economically synthesized at low temperature.