The standard Gibbs energies of formation of intermatallides Fe₆Ge₅, FeGe, FeGe₂ were estimated. Thermodynamic properties of α- and β- solid metallic solutions of Fe – Ge system and spinel solutions of Fe₃O₄ – Fe₂GeO₄ system were determined. The state diagram of Fe – Ge – O system and the potential – рН diagram of Fe – Ge – H₂O system at 25ºС were plotted. The thermodynamic features of the corrosion-electrochemical behaviour of Fe – Ge system was discussed