The corrosion of magnesia–chrome (MgO–Cr 2 O 3 ) brick in molten MgO–Al 2 O 3 –SiO 2 –CaO–Fe t O slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650°C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr 2 O 4 and CaMgSiO 4 phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40mm beneath the permeated layer edge, different shapes of MgO particles are found.