Thermal shock resistance of MgO-C refractories, which were used in the iron and steel industry, by incorporation of pyrolytic carbon black obtained by waste tire pyrolysis was investigated. The effect of porosity on the thermal shock resistance of those refractories as a function of carbon source (graphite or pyrolytic carbon black) was also examined in the current study. The microstructure and fracture surfaces were characterized using the Scanning Electron Microscopy (SEM). Experimental studies showed that refractories produced by the use of pyrolytic carbon black had higher amount of porosity and lower thermal shock resistance than refractories containing flake graphite.