Abstract: The phase equilibrium information of slag plays an important role in pyrometallurgical processes to obtain optimum fluxing conditions and operating temperatures. The smelting reduction of titanomagnetite and ilmenite ores in an iron blast furnace (BF) can form Ti(C,N) particles, causing the increased viscosities of slag and hot metal. HIsmelt has been developed in recent years for ironmaking and does not need coke and sinter. The formation of Ti(C,N) in the HIsmelt process is avoided because the oxygen partial pressure in the process is higher than that in the BF. The smelting of TiO₂-containing ores in the HIsmelt process results in Al₂O₃–MgO–SiO₂–CaO–TiO₂ slag. Phase equilibrium in this slag system has been investigated using equilibration, quenching, and electron probe microanalysis techniques. The experimental results were presented in two pseudo-binary sections, which represent the process of HIsmelt for the treatment of 100% titanomagnetite ore and mixed titanomagnetite+ilmenite ore (mass ratio of 2:1), respectively. The primary phases observed in the composition range investigated include pseudo-brookite M₃O₅ (MgO·2TiO₂–Al₂O₃·TiO₂), spinel (MgO·Al₂O₃), perovskite CaTiO₃, and rutile TiO₂. The results show that the liquidus temperatures decrease in the TiO₂ and M₃O₅ primary phase fields and increase in the spinel and CaTiO₃ primary phase fields with the increase in CaO concentration. The calculation of solid-phase fractions from the experimental data has been demonstrated. The effect of basicity on the liquidus temperatures of the slag has been discussed. The smelting of titanomagnetite plus ilmenite ores has significant advantages to obtain low-sulfur hot metal and high-TiO₂ slag. Experimentally determined liquidus temperatures were compared with the FactSage predictions to evaluate the existing thermodynamic databases.