This work presents results of microstructural characterization of as-cast Co–B alloys. Samples of different compositions were prepared by arc melting Co (min. 99.97%) and B (min. 99.5%) under argon atmosphere in a water-cooled copper crucible with non-consumable tungsten electrode and titanium getter. All samples were characterized by scanning electron microscopy (SEM) in back-scattered electron (BSE) mode, X-ray diffraction (XRD) and wavelength dispersive spectrometry (WDS). A good agreement is observed between the obtained microstructures and those expected by the currently accepted Co–B phase diagram.