Abstract: The samples of magnesia zirconia composite materials were prepared with three kinds of different grades of magnesite, namely Haicheng grade I magnesite, Haicheng grade II magnesite and Xiuyan II grade magnesite (MgCO₃) and desilication zirconium (ZrO₂) as raw materials in order to produce substitute for magnesia−chromite brick of RH refining furnace. The bulk density, apparent porosity, thermal shock resistance and phase composition of the samples were tested. The microstructure of the samples was analyzed. The effects of different sintering temperatures on the sintering properties and thermal shock resistance of magnesia zirconia composite were investigated. The results show that the bulk density was increased, the apparent porosity was reduced, and the linear shrinkage was increased with the temperature increasing. The maximum bulk density of the magnesia zirconia composite prepared with Xiuyan Grade II magnesite and desiliconized zirconia fired at 1700 ℃ was 3.26 g∙cm⁻³. The minimum apparent porosity of the magnesia zirconia composite prepared with Haicheng Grade II magnesite and desiliconized zirconia fired at 1700 ℃ was 5.69%. The c−ZrO₂ solid solution (Zr_0.875Mg_0.125O_1.875) was formed from three different grades of magnesite and ZrO₂. The impurities of SiO₂ and CaO in magnesite were combined with MgO to form low melting point phase, which increased the density of samples and promoted sintering; The CaZrO₃ and c−ZrO₂ (Zr_0.8Ca_0.2O_1.8Zr_0.8) were formed at 1700 ℃ from the magnesia zirconia composite prepared from Xiuyan Grade II magnesite and desiliconized zirconia; The mismatch of the thermal expansion coefficients of CaZrO₃ and c−ZrO₂ with periclase resulted in microcrack toughening and ZrO₂ phase transformation toughening during the cooling process, which made the magnesia zirconia composite sample prepared from Xiuyan Grade II magnesite and desiliconized zirconia at 1700 ℃ have the best thermal shock resistance.