The tensile properties of two MoSi2 alloys with different grain sizes (1 micrometer and 10 micrometer) were evaluated in vacuum at temperatures ranging from 1400 to 1600K and initial strain rates ranging from 1×10-5/s to 1×10-3/s. For the alloy with 10micron grain size an m vale of 0.35 and an activation energy value of 350 kJ/mol were observed in the lower strain rate range while an m value of 0.12 and an activation energy value of 760 kJ/mol were observed in the higher strain rate range. For the alloy with 1micron grain size, a uniform m value of 0.55 and an activation energy value of 160 kJ/mol were observed. Moreover these two alloys showed remarkable ductility (maximum 33%) in the test temperatures. The deformation mechanism and the remarkable ductility are discussed in the light of the microstructural observations through SEM and TEM.