Medium manganese steels (MMnS) represent an important class of novel alloys in the 3rd generation of Advanced High-Strength Steels (AHSS), which are characterized by a manganese content between 3-12 wt.% as well as a multi-phase microstructure. These steels are well-known for outstanding combinations of high to ultra-high strength at relatively high total elongation. Strength and ductility are indeed significantly affected by the amount of retained austenite, its stability, and the related transformation-induced plasticity (TRIP). Due to the possibility of microstructure design, laser-based powder bed fusion of metals (PBF-LB/M) is a promising processing method to tailor the mechanical performance of MMnS. In the present study, a MMnS was processed by PBF-LB/M using various scanning speeds to determine the influence of changing cooling rates on microstructure and mechanical properties. The material was analyzed in the as-built condition by optical and scanning electron microscopy (SEM), hardness measurements, X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). A significant influence of process parameters on the resulting austenite fraction as well as strength and ductility is revealed.