The oxygen solubility in the zirconium-containing iron-nickel melts has been experimentally studied at 1873 K using the Fe–40% Ni alloy as an example. It was shown that zirconium considerably decreases the oxygen solubility in this melt. The equilibrium constant of interaction of zirconium and oxygen dissolved in the Fe–40% Ni melt (logK_{(1)(Fe–40%Ni)} = –6.221), the Gibbs energy of this reaction ( = 223078 J/mol), and the interaction parameters characterizing these solutions ( = –7.16; = –1.25; = 2.16) were determined. The equilibrium constants of interaction of zirconium and oxygen dissolved in the Fe–20% Ni and Fe–30% Ni melts, the Gibbs energy of this reaction, and the interaction parameters characterizing these solutions were calculated for 1873 K. With an increase in the nickel content in melt the deoxidation ability of zirconium decreases. This is due to the fact that, when the nickel content in melt increases, the bond strengths of zirconium with the melt base ( = 4.59·10^–4; = 1.40·10^–10) rise to a considerably greater degree than the bond strengths of oxygen weaken ( = 0.0105; = 0.357).