<p>A series of Fe-based medium-entropy alloys (MEAs) were designed and prepared via Nb and Ta alloying to simultaneously enhance their mechanical and corrosion properties. In the (Fe₂CrNi)_{96−<i>x</i>}Ta₄Nb_<i>x</i> system, the (Fe₂CrNi)₉₁Ta₄Nb₅ composition exhibits a fully eutectic structure with a fine eutectic lamellar spacing of approximately 1.02&#xa0;µm, which enables an exceptional combination of properties. It combines a high compressive yield strength (YS) of 1006.1&#xa0;MPa, a large fracture strain (FS) of 41.9%, and outstanding corrosion resistance in an aggressive ammonium chloride environment. The performance stems from the synergistic effect of the fine eutectic lamellar structure and the dense, protective surface passivation film enriched with Cr, Nb, and Ta oxides. This work presents a design strategy in which a refined eutectic structure in an Fe-based system is effectively targeted to establish a hierarchical defense against both mechanical failure and chemical degradation, providing valuable insights for the development of high-performance MEAs.</p>