This work presents characterization of slag cements and modified oxygen steelmaking slags by pyrometallurgical process.Chemical analysis, SEM and quantitative mineralogical XRD analysis using Rietveld method were applied in slags and slag cements characterization.The combination of various characterization techniques represents an effective contribution to understand the behavior of these non-conventional cements and motivate producers to re-evaluate the ordinary quality control currently applied by clinker and cement manufacturers and users.The results show that the Mg bearing RO phase in steel slag can be classified in different types of FeO-MgO-CaO-MnO and variations, and correlates with potential expansion phenomena.Despite of techniques limitations, elemental microanalysis by SEM contributed to an agile estimative to the hydraulic potential of amorphous phase.