The duplex Ti-45Al-7Nb (at%) alloys with equiaxed fine grains were prepared by powder metallurgy method. The high temperature mechanical properties of the alloys at 900, 950, and 1000 °C under the strain rates of 1×10^-3, 1×10^-4, and 5×10^-5 s^-1 were investigated, and the corresponding deformation mechanism was also discussed. Results show that the tensile strength is decreased whereas the elongation is greatly increased at elevated temperatures or under decrescent strain rates. Since the small grains are easy to achieve deformation and coordination, the elongation of the small grain alloys is significantly higher than that of coarse grain alloys. The alloys form a large number of voids at the fractures after high temperature tensile. Long cracks perpendicular to the tensile direction are formed at the front fracture. Besides, the grain boundary sliding, grain twinning, and dynamic recrystallization also lead to the deformation of alloys, thus improving the microstructure ductility.