Use of magnesium in industry, particularly inautomobile industry is consistently increasing. Allknown casting processes including investment castingcan be used for production of magnesium castings.Magnesium, however, reacts practically with allinvestment casting refractories, from which moldsare made of. The research work was carried out a) toinvestigate the degree of reactions between thevarious refractory materials and the magnesium alloyAZ91E; b)to find new techniques to reduce thesereactions and c)to provide a better understanding ofthe mold-metal reactions in magnesium investmentcasting Fused alumina,fused silica, molochite,zircon,yttria, zirconia and fused magnesia were the studiedceramics. Results of the experiments are discussedand conclusions are drawn on the relative reactiontendency of studied refractories and other factorsaffecting the mold-metal reactions.