A novel Al₂O₃-based refractory aggregate with closed-pore structure was fabricated utilizing superplasticity with submicro-sized Al₂O₃ and MgO as raw materials, and SiC as a high temperature pore-forming agent. The effect of MgO on porosity, phase composition and microstructure of the refractory aggregate has been investigated. For comparison, the common Al₂O₃-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al₂O₃-based refractory aggregate increases as the content of MgO increases. When the content of MgO is 15 mass%, the closed and apparent porosities are 14.5% and 1.1%, respectively. The main phase compositions are Al₂O₃ and MgAl₂O₄. The formation mechanism of closed pores is that the fineª²crystalline-grain Al₂O₃ ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al₂O₃ ceramic, the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then, the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabricated closed pore Al₂O₃-based refractory aggregate is better than the common refractory aggregate and porous ones.