Nanocrystallines Co3O4 with the particle diameter of 3 nm are prepared and tested as active electrode material for an electrochemical supercapacitor. The results of characterization indicate that the grain size of this material is very small; the specific surface area is very high (192 m2/g); the distributions of pore diameter are desirable and effective; furthermore, the agglomeration problem among small particles was solved to a certain extent. The electrochemical tests show that the electrode prepared with the Co3O4 exhibits distinct characteristic of capacitance and very high specific capacitance of 365-401 F/g. Additionally, the main attribute of capacitance, namely supercapacitance, was also testified.