The redox properties of monolayer-protected gold nanoclusters (MPCs) are considered from both the theoretical and experimental viewpoints. The "absolute standard redox potential" ([E-Z/Z1(0)](abs)) of MPCs is first derived from electrostatic considerations. A linear dependence of the absolute standard redox potential on the valence state of MPCs is theoretically predicted and verified experimentally. By employing ferric in ium/ferrocene (Fc(+)/Fc) as a reference redox couple, the average valence state of MPCs at a given potential can be estimated.