Abstract: To enhance the overall performance of magnesia-carbon bricks for ladle slag lines, this study introduced light-burned ascharite powder into a conventional formulation. Its effects on the physical properties, high temperature modulus of rupture, thermal shock resistance, and slag resistance of the bricks were systematically investigated. Results demonstrate that the composite addition of light-burned ascharite and metallic aluminum powder exhibits superior high temperature modulus of rupture, slag resistance, and thermal shock resistance compared to the formulation with ascharite alone. The synergistic effect is attributed to two mechanisms. The first involves aluminum powder, which at low to medium temperatures forms Al₄C₃ fibers, subsequently oxidized to Al₂O₃ and transformed into spinel. This process effectively fills and seals pores through the associated volume expansion and solid-phase deposition, thereby improving the medium-to-high temperature strength and slag resistance. Simultaneously, an appropriate amount of light-burned ascharite powder generates a dispersed magnesium borate liquid phase at high temperature, which promotes sintering densification, alleviates thermal stress, and strengthens the matrix through pinning effect, thereby significantly enhancing the high-temperature performance and thermal shock stability.