<p>We investigated the effects of the representative gangue or refractory components MgO and Al₂O₃ on the FeO reduction mechanism and chemical reaction kinetics in synthetic slags simulating the upper part of an electric smelting furnace (ESF) at 1873 K (1600&#xa0;°C) to produce hot metal using a hydrogen-reduced iron ore for CO₂ mitigation. The experiments were conducted in a high-frequency induction furnace to facilitate the smelting reduction reaction, and the FeO reduction rate in the slag was analyzed through an <i>in-situ</i> off-gas analysis. Additionally, interval sampling was applied to observe changes in chemical composition of slag over time during smelting reduction. The experimental results revealed that the FeO reduction reaction in molten slag by solid carbon proceeded in three distinct stages in terms of chemical reaction kinetics: (i) incubation, (ii) steady state, and (iii) degradation. During the incubation period, the duration varied depending on the mass ratio of MgO to Al₂O₃, which was interpreted to be a result of the influence of the slag’s physical properties on the nucleation and growth rate of bubbles around the carbon. In the steady state period, experiments using a magnesia refractory exhibited relatively higher reduction rates for all slag compositions, whereas those using an alumina refractory showed a lower reduction rate. This was attributed to the dissolution of Al₂O₃ from the refractory into the slag, where it acted as a network former, increasing the slag viscosity and slowing the reduction rate. The current study provides fundamental data for optimizing slag design to achieve rapid FeO reduction in ESF. Based on these findings, it is expected to contribute to improving Fe yield and enhancing slag sustainability.</p>