Effect of Y 2 O 3 –MgO addition on heterogeneous precipitation-thermal reduction synthesis and the sintering of Fe–Mo/Si 3 N 4 powders has been investigated. It was found that the whiskers-like β-Si 3 N 4 , good wettability phases on Si 3 N 4 surface, and high toughness Fe phase appeared in Fe–Mo/Si 3 N 4 cermets with Y 2 O 3 –MgO additives. The results show that Y 2 O 3 –MgO additives can effectively optimize the microstructures of Fe–Mo/Si 3 N 4 cermets, and improve the material mechanical properties. Therefore, it indicated that Y 2 O 3 –MgO additives can be used for strengthening of sintered cermets, and the dual function of whiskers self-toughening and different metal-composition toughening can be achieved in Fe–Mo/Si 3 N 4 cermets with Y 2 O 3 –MgO additives.