In this paper, we studied the directly interaction between nuclease Pl and CuCl2 in aqueous solution by visible absorption spectra. As a result, the zinc ion in the active site of nuclease Pl can be replaced by additional Cu(II). At the the same time, Cu(II) entered into the active site of enzyme forming the correspondent derivatives of "Cu(II)-Pl". The variety of pH value influenced the types of derivatives and the enzyme activity.