The stagewise substitution equilibria AuCl- 4 + iOH– = AuCl4 – i OHi - + iCl–, βi in aqueous solutions at 50 and 80°C (I = 1 mol/L NaCl) have been studied. The equilibrium constants log β1 = 7.26, log β2 = 13.98, log β3 = 19.66, log β4 = 24.78 (50°C); log β1 = 6.89, log β2 = 13.13, log β3 = 18.43, and log β4 = 23.30 (80°C) have been determined. They are lower than the same constants at 25°C. The spectra of complex speciesspecies at 80°C have been calculated, and the heterogeneous equilibrium 0.5Au2O3 xH2OS + OH– = Au(OH)4 - + 0.5xH2O of the red Au2O3 · xH2OS species at 80°C has been studied, logKS = 3.7 ± 0.2. The obtained results may be useful in geochemistry and the synthesis of gold nanoparticles.