MgO–CaO refractories added with different sized ZrO2 powders were sintered at 1600℃, the effect of the ZrO2 powders on performance of MgO–CaO refractories was investigated. The results showed that the densification of the MgO–CaO refractories was appreciably promoted when a small amount of ZrO2 was added owing to the formation of small size CaZrO3 facilitated to sintering, and the densification was promoted further with increasing the amount of ZrO2 due to the volume expansion caused by the reaction of the added ZrO2 and CaO to form CaZrO3 in the refractories, and the addition of nano-sized ZrO2 was more effective. The thermal shock resistance of the MgO–CaO refractories was improved by modification of the microstructure due to the formed CaZrO3 particles that predominately located on the grain boundaries and triple points in the whole microstructure, and the addition of nano-sized ZrO2 was more effective attributed to its well dispersion and the critical addition amount was effectively decreased to 6%. The slaking resistance of the MgO–CaO refractories was appreciably improved by addition of ZrO2 due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of microstructure, the nano-sized ZrO2 addition was more effective due to its higher activity. The slag corrosion resistance of the MgO–CaO refractories was enhanced by addition of ZrO2 due to the increase of the viscosity of the liquid phase and thus inhibited further penetration of slag at elevated temperatures.