To reduce environmental impact of cement production, granulated blast furnace slag (GBFS) can be used as a cement clinker substitution. Its reactivity of can be increased by adequate fine grinding. The impact of different conventional laboratory-scaled mills (ball mill, vertical mill, and roller press) on the material properties was researched. Granulometrical, structural, and calorimetrical investigations were done. It could be demonstrated that at the same fineness the grinding unit does not significantly influence the cement performance like hydration heat release and compressive strength. On the other hand, particle properties like particle size distribution, particle shape, and thus workability characteristics of composite cements have been changed.