It has been found that the dispersion of phases in copper-nickel sulfide-metal alloys influences their electrochemical properties. X-ray diffraction and optical and electron microscopy have been used to study structural characteristics of the samples prepared by crystallization of sulfide melts at different rates of 10÷103 K/s. High-rate cooling of a converter matte leads to the formation of nonequilibrium sulfide phases and a metallic component dissolved in these phases. The electrochemical oxidation of copper-nickel sulfide alloys has been studied by voltammetry with a linear potential sweep. The data point to a reduction of the limiting oxidation currents of the sulfide alloys prepared by high-rate cooling. The compositions of the intermediate phases and solid products of the electrochemical oxidation, which form the passivating layer, have been determined. The electrolysis of dispersed sulfide alloys allows performing the process at low densities of the current and, thus, the diffusion limitations have been removed.