The electroformation of a Cu2S phase, obtained by sulfidization of a thin film of copper placed by the spin-coating technique onto the gold surface of a gold/quartz crystal that is part of an electrochemical quartz crystal microbalance (EQCM), was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry. The electrolytic medium employed was a bisulfide-containing aqueous buffered solution (pH 9.2). CV parameters showed that the formation of the Cu2S phase occurred by means of an irreversible diffusion-controlled mechanism, where a first uncomplicated electron transfer was the rate-determining step. The EQCM data showed that the initially formed phase was Cu2S, which was later oxidized to nonstoichiometric compounds (Cu(2-x)S) and CuS. Furthermore DeltaQ/Deltam data analysis established that the electron,reaction valence (n) was close to 2 for all electrochemical processes where Cu/S compounds were involved. The nucleation and growth mechanism (NGM) of the Cu2S Phase corresponded to a bidimensional instantaneous mechanism containing two contributions, one controlled by diffusion and the other controlled by charge transfer. Atomic force microscopy (AFM) revealed that the Cu2S Phase electroformed on the gold/crystal quartz electrode was deposited as hemispherical particles (sized between 40 and 130 nm) on the terraces and in the cavities present in the gold film.