Abstract: A periclase-hercynite brick was prepared via reaction sintering at 1600℃ for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe²⁺, Fe³⁺ and Al³⁺ ions in hercynite crystals migrate and react with periclase to form (Mg_1-xFe_x)(Fe_2-yAl_y)O₄ spinel with a high Fe/Al ratio. Meanwhile, Mg²⁺ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg²⁺ migration leads to the formation of (Mg_1-uFe_u)(Fe_2-vAl_v)O₄ spinel with a lower Fe/Al ratio and results in Al³⁺ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.