Abstract: Isothermal thermogravimetric analysis was used to study the reduction process of solid/liquid wustite by hydrogen. Results show that wustite in both states can be reduced entirely at all temperatures. The thermal and kinetic conditions for the hydrogen reduction of molten phases are better than those when the reactants and products are in the solid state, with a higher reaction rate. The hydrogen reduction of different wustite phases fits the Mampel Power model (power exponent n = 1/2) well, and this model is independent of the phase state. The average apparent activation energies of the reduction process calculated by the iso-conversional method are 5.85 kJ·mol⁻¹ and 104.74 kJ·mol⁻¹, when both reactants and products are in the solid state and the molten state, respectively. These values generally agree with those calculated by the model fitting method.