In-situ angle dispersive x-ray diffraction (ADXRD) with synchrotron radiation source is performed on an ultra-high temperature refractory of MoSi2 and Mo5Si3 by using a diamond anvil cell (DAC) at room temperature.While the pressureinduced volume reduction is almost constant,the value of the bulk modulus increases with the decrease of molybdenum content in the system.According to the Brich-Muaghan equation,the bulk modulus 222.1 (2.1) GPa with its pressure derivative 4 of MoSi2,and the bulk modulus 308.4 (7.6) GPa with its pressure derivative 0.7 (0.1) of Mo5Si3 are obtained.The experimental data show that MoSi2 has distinct anisotropic behavior,Mo5Si3 is less anisotropic than MoSi2.The result shows that MoSi2 and Mo5Si3 have the structural stabilities under high pressure.When the pressure reaches up to 41.1 GPa,they can still maintain their body-cantered tetragonal structures.