The impact toughness of M951 alloy is investigated in temperature range between 20°C and 800°C. The results show that the impact toughness of samples impacted at 600°C shows highest impact toughness value, the impact toughness value drops sharply when the samples impacted at 760°C. In addition samples impacted at 800°C show the higher impact toughness than that of samples impact at 760°C. The scanning electron microscope observations show that cracks initiate at carbides particles due to high stress concentration, which leads to low impact toughness value at 20°C. The dimples which can absorb more energy are formed during the impact at 600°C. The samples impacted at 760°C show lowest impact toughness. Additionally, the dimples nucleation, growth and coalescence are the major fracture mechanism at elevated temperature.