This paper investigates the new phases formation in the magnesia-spinel, magnesia-zirconia-cal- cia and magnesia-hercynite refractory products as a result of their reaction with kiln hot meal and cement clinker (both rich in SO3 and Cl ions) at the temperature range 1200°C - 1450?C. The labor- atory corrosion tests were conducted by means of pulverous method and by special coating test. The phase identity of the products as well as the mixes after corrosion tests was established by powder X-ray diffraction method. The microstructure development of the contact zones between coating and the products were studied using scanning electron microscopy SEM with EDS spectroscopy. The differences in the reactions proceeding between the phases of the test bricks and the phases of kiln hot meal and cement clinker in dependence on the temperatures have been discussed.