Superconductivity of n-type superconductor Nd1.85Ce0.15CuO4-y (NCCO) by electrochemical oxidation is reported for the first time and the cyclic voltammogram curve for NCCO as working electrode is presented. Investigations indicate that after oxidation, superconductivity of NCCO is improved: Tc is raised from 20 K up to 26 K, the superconducting volume fraction is increased also. The valence electronic states of oxygen and copper in NCCO are studied by x-ray photoelectron spectroscopy. It is found that the Cu-2ps/2 peak shifts to the higher binding energy side about 0.4 e V, which indicates that the valence-state of copper ions is risen up after oxidation.These results imply that hole-carriers exist in n-type superconductor.