A novel and facile method for the synthesis of CuO nanocrystals with various morphologies is reported. The synthesis involves the convenient hydrothermal decomposition process of the Cu(COOH)(2) in the mixture of dimethyl sulfoxide (DMSO) and H2O. The spherical, rodlike, and leaflike CuO nanocrystals are prepared by varying the concentration of water. The capacitance of CuO products was determined by cyclic voltammetry.