Abstract: To understand the formation and growth mechanism of the magnetite phase during the fluidized reduction of hematite, a high-purity hematite ore was isothermally reduced using a 20vol% CO-80vol% CO₂ gas mixture in a micro-fluidized bed to examine the process of the selective conversion of hematite to magnetite. The micro-structural characteristics of the magnetite phase were investigated using scanning electron microscopy (SEM) and the Brunauer, Emmett, and Teller (BET) method, and the thickness of the magnetite layer was measured and evaluated using statistical analysis. The experimental results showed that the fresh magnetite nuclei were dense needles of different lengths, and the original hematite grains became porous after complete reduction to the magnetite phase. The thickness of the magnetite layer increased with an increase in reduction temperature and reduction time. The growth kinetics of the magnetite layer was investigated, and the value of the activation energy E was estimated to be 28.33 kJ/mol.