Mg2Si/Mg composites, using Mg and Si powders as the starting raw materials, were produced via the solid-state synthesizing process and the hot forging process. The friction coefficients of these composites increases with increase in the content of Mg2Si. On the other hand, Mg2Si/MgO/Mg composites, using Mg and SiO2 powders as the starting raw materials, were produced via the same processes as those of Mg-Si powder. The friction coefficients of Mg2Si/MgO/Mg composites reduced in comparison with that of Mg2Si/Mg composites. It is considered that the "offensive" effect of Mg2Si was reduced by the "mild offensive" effect of MgO.