MgO-heat insulating bricks were produced using high quality sinter- MgO, 25 % or 35 % combustible materials and 20 % spinel (M-Sp/I) or alumina (M-Sp/II) additives. For sufficient strength MgSO4 was added in amount of 7.5 %. Petroleum coke and saw dust mixture was used as combustible material. The optimal heating profile was determined with the help of thermo gravimetric analyses. Hematite fines were used as sintering aid. The formed samples were sintered at 1500 and 1600 degreesC. The thermal conductivity curves and micro-structure of the samples were similar to those of the reference sample.