Nanostructured MnO2 thin films were synthesized via an electrodeposition method assisted by ultrasonic treatment. Applying the ultrasonic treatment during or after electrodeposition, the films develop a variation of microstructures of distinct properties and characteristics. As a result, the MnO2 films show improved specific capacitances and cycling performance. The MnO2 film produced by electrodeposition followed by ultrasonic treatment exhibits a microstructure of free-standing nanowires with diameters less than 10 nm and the highest specific capacitance of 369 F g(-1) in this investigation, which is fairly stable after successive cycles up to 1000 cycles. The enhanced capacitance performance of the MnO2 films suggests a great potential of the electrodeposition assisted by ultrasonic treatment for supercapacitor manufacturing.