Two types of magnesium-aluminate spinels, one commercially available as preformed powder and the other prepared from cheaper precursors by the sol-gel route as a semidried reactive mass, were characterized in terms of particle size distribution, XRD phase evolution and chemical composition. These two were incorporated in a high alumina based refractory castable in different concentrations and fired at elevated temperatures. Those preformed and in situ spinel bonded castables were characterized in terms of bulk density, apparent porosity, cold crushing strength, thermal shock resistance, volume shrinkage, flexural strength, XRD, SEM, EDS and slag corrosion resistance test to understand the effect of both kinds of spinel in the castable composition. © 2003 Elsevier Ltd and Techna S.r.l. All rights reserved.