The preliminary results of the application of open-celled glassy-carbon foam (Cof) in magnesium matrix composites processed by the powder metallurgy method were presented. For the component consolidation, compaction with vertically-torsional vibration and hot-pressing were applied. For the material characterization, the microstructure examination LM and SEM with EDS was employed and also, the porosity and microhardness were measured. An influence of the carbon foam cells’ size on the composite porosity and microhardness was revealed. Additionally, a generation of a few micrometer thin and differently shaped MgO inclusions was observed. Differences in the oxide phase amount, size and shape in the magnesium matrix measured by the quantitative metallography method in the cross-sectioned composite elements were stated. With an increase of the distance from the composite roller top, an increase of the MgO content and microhardness was noticed.