Abstract: In the present paper ESR spectra of six acidic phosphates (phosphonates) co- pper (Ⅱ) complexes in solid state at room temperature have been examined, and their ESP spectral parameters in THE at low temperature have been determined. The bonding parameters and difference of reducible level of these complexes were calculated. The bonding characterization of these copper (Ⅱ) complexes were dis- cussed. The result shows that the in-plane σ-bond in these complexes plays an important role, but the action of in-plane π-bond on bonding of these complexes may not be also neglected.