Protein CopC from a pathogenic bacterium Pseudomonas syringae pv. tomato (CopC) is one of four proteins (CopA, B, C and D) coded on the copper resistance operon (cop). Using fluorescence measurements, differential optical spectra, methods of cyclic voltammetry and studing the kinetics of oxidation of ascorbic acid, we investigated the possibility of protein CopC binding with Au III ion. The results showed that the Au III ion can be bound with CopC in the ratio of 2: 1. The apparent binding constants k 1 and k 2 are 3.68·10 3 and 3.92·10 4 L mol −1 , respectively. Binding with Au III ions does not result in considerable conformational changes of protein CopC.