Electrodeposited cobalt hardened gold is widely used for electronic applications. The aim of this study was to investigate and optimize the performances of the plating electrolyte (cathodic efficiency and deposition rate) and the composition of the Au-Co coating. A four variable Doehlert experimental design was applied to this optimization and validation was carried out by means of statistical analysis. In a second step, the 'optimal' Au-Co electrodeposit was examined by spectroscopy techniques (GDOES, XPS).