In order to clarify the effect of spherical light-weight aggregates addition on properties of Al₂O₃-SiO₂ system castables, adopting A70 mullite traditional light-weight aggregates and A70 mullite spherical light-weight aggregates, bauxite homogenization powder, microsilica, calcium aluminate cement as main raw materials, light-weight Al₂O₃-SiO₂ system castables were prepared by replacing conventional light-weight aggregate with spherical light-weight aggregates. The effects of spherical light-weight aggregates addition on workability, mechanical properties of castables after heated at different temperatures were researched; the microstructure of the aggregates was analyzed by SEM. The result shows that the introduction of spherical light-weight aggregates can significantly improve the flowability and reduce the water addition of the castables. Water demand of the castable is reduced from 18% with the conventional light-weight aggregates to 14% with spherical light-weight aggregates. In addition, light-weight castables prepared by spherical aggregates can keep the same workability within a wider range of water addition. Therefore, spherical aggregates are user-friendly. The introduction of spherical light-weight aggregates is favorable to packing density and mechanical properties of castables, such as cold crushing strength, cold modulus of rupture, hot modulus of rupture at 1 200 ℃.