Properties of mixtures of Portland cements and "waste steel foundry dust (WSFD)" from Czech steel works were examined. It was found that WSFDs are formed by microporous clusters of spherical particles of iron oxides, ranging in size from 10 to 100 nm. The content of ZnO in WSFD affects markedly the hydration of cement + WSFD mixtures both in solidification time and strength development. Properties of WSFD are very similar to those of very fine silicon flue dusts formed during Si and FeSi production. Cement + WSFD mixtures show long term strength stability and low heavy metals leaching even at WSFD content of 70-80wt.% The above results document the perspectives of WSFD solidification, disposal and the use of this waste material as a new additive to building materials.