Alumina magnesia castable crucible specimens were prepared using tabular corundum, fused magnesia powder, fused spinel powder, and Al₂O₃ micropowder as main starting materials, batching, mixing, shaping, and drying. Slag resistance was determined by static crucible method at 1 600 ℃ for 3 h adopting two ladle slags with different basicities (3.40 and 1.03). The corrosion and penetration indexes and microstructure characteristics of the specimens after slag resistance test were analyzed to study the corrosion behaviors of the two slags to alumina magnesia castables. The results show that the corrosion of the low basicity slag to alumina magnesia castables is much more serious than that of the high basicity slag for that their reactions with castables form different products; for the low basicity slag, the multi-phase coexistence of CA₆ and compounds of CaO-Al₂O₃-SiO₂ in the materials together with volume expansion caused by the formation of CA₆ intensify the slag corrosion and penetration; for the high basicity slag, the reaction between slag and castables generates a CA₂ dense layer and a large amount of in-situ MA in the interface, reducing the slag corrosion to the materials effectively.