Based on the pore size design of microporous aggregate by numerical simulation applying porous media model, α-Al₂O₃ micropowder, industrial Al₂O₃ fine powder, α-Al₂O₃ micropowder+CaCO₃ fine powder were used as starting materials, respectively, to prepare three microporous corundum aggregates specimens, named as A1, A2 and A3. Two lightweight Al₂O₃-MgO castables were prepared by selecting A1 or A3 as aggregate with ム.6 μm of average pore size, then performances of castables with microporous corundum aggregates and castables with tabular corundum aggregates were compared. The results show that: (1) the microporous corundum aggregates with bulk density of 3.1-3.5柠·cm^-3, apparent porosity of 5%, closed porosity of 8%-13%, and smaller thermal conductivity at 800 ℃ than tabular corundum, can be prepared by sintering at above 1 800 ℃; (2) compared to normal Al2O3-MgO castables, the two lightweight Al₂O₃-MgO castables have lower bulk density and higher apparent porosity; lower change rate in dimensions and higher strength firing at 1 500 ℃; and lower thermal conductivity at 600 and 800 ℃; (3) compared to normal Al₂O₃-MgO castables, Al₂O₃-MgO castable with A1 has higher penetration index, and that with A3 has higher corrosion