Calcium hexaaluminate (CA6) materials have garnered attention for their potential use as lining materials in metallurgical furnaces during the steel-making process. The present work explored the effects of M2O5 (M = Nb, Ta) on the steel corrosion behaviour of calcium hexaaluminate combined with the evolution of physical properties. The introduction of M2O5 (M = Nb, Ta) was proved to be advantageous in mitigating the emulsification of CA6 material in the molten steel, and the increase in the densification of emulsion layer could prevent CA6 materials from further steel corrosion and penetration. The improved steel corrosion resistance of CA6 materials was attributed to the optimization of the physical properties facilitated by the formation of defects and the in situ phase. In addition, the reduction in the wettability between the CA6 materials and molten steel served to diminish the reactivity of the interface reaction. This work determined the corrosion behaviour and corrosion mechanism of the CA6 materials in molten steel and provided a new research route for designing CA6 materials with improved corrosion resistance to molten steel.