In this work, high specific capacitance of Mn3O4 is successfully synthesized via ultrasonic and hydrolyzation at room temperature. The crystal structure, phase and the electrochemical performance are dependent on the preparation conditions, such as ultrasonic time, reaction temperature, and the organic solvent used, etc. The effect of ultrasonic time and the presence of various solvents are well discussed in the crystal growth mechanism and improved supercapacitor performance of Mn3O4. The almost 100% yielded Mn3O4 nanoparticles via ultrasonication for 6 h at room temperature exhibit high specific capacitances (261 F g(-1) at 0.4 Ag-1 and 140 F g(-1) at 40 Ag-1) as well as excellent cycle life. The high yield and convenient synthetic route at room temperature make readily scaled-up production of transition metal oxides for electrochemical applications. (C) 2012 Elsevier B.V. All rights reserved.