Abstract: To improve the utilization rate of magnesite tailings, reduce the production cost of magnesia-based refractories, and minimize environmental pollution caused by magnesite tailings, magnesia-based composites were prepared via a pressureless solid-phase reaction sintering method using light-burned magnesite tailings powder as the raw material, yttrium oxide as an additive, and glycerol as a binder. The effects of Y₂O₃ addition (with mass fractions of 0, 1%, 2%, and 4%) on the phase composition, microstructure, bulk density, apparent porosity, cold modulus of rupture, and thermal shock resistance of the samples were investigated. The solid solution of Y₂O₃ distorts the forsterite lattice, enhances the ion diffusion rate, and promotes the migration and rearrangement of forsterite particles within the lattice, thereby filling pores and gaps and improving the density of the samples. Furthermore, yttrium oxide reacts with the impurity phases CaO andSiO₂ to form a high-melting-point phase, Ca₄Y₆O(SiO₄)₆, the presence of which improves the strength of the samples. The sample with 2% (mass fraction) Y₂O₃ exhibits the best comprehensive performance, with a bulk density of 3.04 g/cm³, apparent porosity of 3.82%, linear shrinkage of 14.93%, cold modulus of rupture of 94.33 MPa, and residual strength retention rate of 89.64%. The effect of yttrium oxide on the thermal shock resistance of the magnesia-based composites was well explained using a simplified second thermodynamic factor.