A series of experiments of electro-refining of copper in electrolytes of different composition have been carried out in laboratory and industrial conditions. Statistical processing of ex-perimental data revealed a regression dependence of sulfuric acid concentration on copper and nickel concentrations in the electrolyte, determining its optimal composition. The obtained formula allows to maintain in the process of electrolytic refining of copper the optimal level of acid concentration at any concentrations of copper and nickel, providing the minimum possible specific power consumption for the production of electrolytic copper of the highest grade (M00k).