Microstructures of unused and used magnesia-chromite (MgO + Mg and magnesia-spinel (MgO + MgO-Al^Os) refractory bricks were characterized. The purpose was to compare different products for evaluation as replacement bricks, and to minimize refractory wear. The way in which the different phases are assembled in the microstructure signifıcantly determines the resulting corrosion behavior. Microstnıctural analyses were performed to identify these phase composures. Industrially worn bricks were examined by optical reflected light microscope, electron microscope (SEM) coupled with energy dispersive X-Ray microanalysis system (EDS) and X-Ray diffraction (XRD) to understand the corrosive reaction paths. in some of the chromite containing bricks iron-rich rims were observed, while the domestic brick had no such feature. These iron-rich rims were examined using SEM-EDS. it was found that the counter-diffusion of Fe and Mg were responsible for their formation. Magnesia-spinel bricks contain low melting calcium aluminates as bond phases in the microstructure, forming a threat to service performance. A statistically designed set of experiments was conducted to investigate the effects of time (0.5-2.0 hours), temperature (1500-1550°C) and clinker chemistry (40-60 wt.% iron öre addition) on the depth of penetration of clinker melt into a magnesia-chromite brick. These experiments indicated that the addition of iron and its interaction with temperature factor are signifıcant. At the highest temperatures and iron öre addition quantities the corrosion depth reaches up to 1200 (im. Postmortem microanalysis of industrially used bricks revealed alkali attack in addition to creep as main destruction mechanisms for brick. Traces of elements like zinc and vanadium were observed and thought to originate from the use of waste derived fuels ör fuel oil fıring for obtaining the main name after long kiln shutdowns.