Processes involving gold(I) complexes were studied in sulfite–thiourea (TU) solutions. It is shown that at pH >5 the complex [AuTU2+] undergoes irreversible decomposition followed by deprotonation and formation of a solid phase. From the data of pH in mixed solutions, the equilibrium constants were evaluated: Au(SO3)23-+iTU⇌Au(SO3)2-iTUi2i-3+iSO32-, log10β1 = −1.2, log10β2 = −3.6. Some aspects of the anodic dissolution of gold in mixed sulfite–thiourea solutions are considered. With the help of the carbonate buffer system the change of the anodic current density ja was studied at high pH; ja (pH) has a maximum at pH 11.6–11.9 for Ea = 0.3–0.6 V (vs. NHE). At pH > 12.0, the ja values decrease sharply. Possible mechanisms of anodic gold dissolution, as well as the role of sulfite, are discussed.