The superplastic properties of a engineering TiAl based alloy with a duplex microstructure were investigated with respect to the effect of testing temperatures ranging from 950 degrees C to 1075 degrees C and strain rates ranging from 8 x 10(-5) s(-1) to 2 x 10(-3) s(-1). A maximum elongation of 467% was achieved at 1050 degrees C and at a strain rate of 8 x 10(-)5 s(-)1. The apparent activation energy was calculated to be 345 kJ/mol. Also, the dependence of the strain rate sensitivity values on strain during superplastic deformation was examined through the jump strain rate tests, and microstructural analysis was performed after superplastic deformation. It is concluded that superplasticity of the alloy at relatively low temperature and relatively high strain rate results from dynamic recrystallization, and grain boundary sliding and associated accommodation mechanism is related to superplasticity at higher temperature and lower strain rate.