Using active site model molecules consisting of approximately 100 atoms, the reduction potentials of five type-1 Cu centers in cucumber stellacyanin, fern dryopteris crassirhizoma plastocyanin, Met148Gln rusticyanin, wild type rusticyanin, and Met148Leu rusticyanin were calculated with a heterogeneous conductor-like polarizable continuum model and the B3LYP/6-311++G(2df,p) method. The results are 242, 366, 522, 667, and 825 mV, respectively, in good agreement with experimental values 260, 376, 563, 667, and 798 mV. Ligand interaction ( approximately 250 mV) and solvation effect ( approximately 250 mV) are found to be the main determinants of the relative E(0) of these five type-1 Cu centers.