The effects of the content of molybdenum on the dynamic properties of tungsten heavy alloys were investigated. Increase in mechanical properties was observed in molybdenum-added tungsten heavy alloys, due to the refined microstructure. On the other hand, decrease in mechanical properties was also observed in the alloys with high molybdenum concentrations, due to the decreased strength of the matrix phase and the precipitation of an intermetallic phase. Hopkinson bar dynamic test under strain rates ranging from 2000 s-1 to 8000 s-1 at room temperature revealed that the flow stress of tungsten heavy alloys depended strongly on the strain, strain rate, and the content of molybdenum. The variation of flow stresses was caused by the competition between work hardening and heat softening in the materials at different strain rates. The high temperature strength of the matrix phase was increased by the addition of molybdenum, which enhanced the strength of the tungsten heavy alloys in high strain rate test.