As an alternative selection of electrocatalytic surface modifier, the electrochemically generated copper oxides is reinvestigated by using cyclic voltammetry (CV), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Interesting phenomena have been found, which indicate that the electrodeposition from the Cu 2+ solution under cyclic voltammetric conditions can generate a transparent Cu(OH) 2 crystalline on the surface of glassy carbon electrodes, and this crystalline can be further transferred to a novel cubic opaque CuO crystalline of about 300 nm in size by second step of cyclic voltammetry in pH 12 NaOH solution. The final electrode (denoted as nano-CuO/GCE) can catalyze the oxidation (as well as the reduction) of H 2 O 2 in basic solutions. It shows pH dependent three-part catalytic mechanism in the range from pH 7 to pH 14. In 0.10 mol/L NaOH solution, the amperometric response at 0.15 V (vs. SCE) can give a current sensitivity as high as 139 mA/(mol•L -1 ) in the rage of 5.0×10 -7 -6.0×10 -4 mol/L with a lower detection limit (s/n=3) of 2.5×10 -8 mol/L, and a current sensitivity of 78.4 mA/(mol•L -1 ) in the rage of 6.0×10 -4 -2.0×10 -3 mol/L. This electrode also has excellent reproducibility and stability. The mechanisms for the two steps of preparation and the catalytic reactions are proposed. The nano-CuO crystalline modified electrode may have more applications in the field of electrochemical sensing.