Abstract: The effect of chemical composition on the fracture toughness and microstructure has been studied. The results have shown that the cermet is of high fracture toughness value when the contents of tungsten carbide and molybdenum are 10% and 15% respectively. The fracture toughness decreases linely with increasing the content of NbC,TaC or (Nb, Ta) C. Low wettability of metals for ceramics is the main reason of low fracture toughness value.