The structure and phase composition of synthesized copper(I) sulfide are studied. It is shown that, both chalcocite (Cu2S) and jarleite (Cu31S16) phases can form in the copper sulfide crystallization. Jarleite is characterized by a deficit of copper in the crystal lattice and a deviation from the stoichiometric composition. The formation of jarleite is associated with the crystallization of the copper metal phase. The crystal lattice parameters of the synthesized phases are calculated. It is shown that they correlate with the database of International Center for Diffraction Data. The electrochemical oxidation of specimen in the sulfuric acid solution is carried out. It is found that at a current density of 1000 A/m2 and a concentration of 100 g/dm3 H2SO4, the electrochemical dissolution of copper sulfide proceeds with the formation of passive film of slightly soluble products due to the oxidation of copper(I) sulfide to copper(II) sulfide. In addition, in the course of oxidation, intermediate nonstoichiometric sulfides (Cu1.74S, Cu1.8S, Cu1.6S, and CuS) form in the following order: Сu2S (Cu31S16) → Cu1.8S → Cu1.74S → Cu1.6S → CuS → S + Cu2+. The process is accompanied by the transition of copper cations into the solution. As elemental sulfur and copper sulfides are accumulated on the specimen reactive surface, the electrochemical oxidation rate decreases due to slow removal of the products and slow supply of the reagent to the reaction zone.