Experiments were carried out to study the chemical interaction between coal slags and Zr-bearing chromia refractory. The results showed that the corrosion was related to the slag viscosity : the lower the slag viscosity was, the greater the amount of slag was penetrated under CO/CO2 reducing gas mixture. Small refractory cores taken after corrosion experiments were polished and examined by scanning electron microscopy and X-ray diffraction. We observed fayalite crystals probably from the slag penetrated and Cr2O3 and ZrO2 crystals of refractory.