Abstract Phenolate bridged binuclear Cu(II) complexes were used to monitor the contribution of the endogenous bridging ligand to the resonance Raman spectrum of the oxygen transport protein such as hemocyanin. From the excitation profile of the intensity enhanced phenolate v c-o the phenolate-to-Cu(II) charge-transfer transition of the four studied complexes has been located between 380 nm and 430 run, similar to the low-temperature absorption band in the hemocyanin spectra. By approaching the exciting laser frequency to this electronic transition, the whole spectral range 1250–1650 cm −1 is strongly intensity enhanced and considered as the typical feature of this kind of phenolate bridged Cu(II) complexes. Comparison to mononuclear analogues pointed out no significant differences of the resonance enhanced Raman lines. The results are discussed in relation to the resonance Raman spectra of hemocyanin.