Superplastic mechanical behavior of Ti-48Al-2.3Cr-0.2Mo (at%) alloy with deformed microstructure was investigated at temperatures ranging from 800 to 1100 oC with strain rates between 5′10-5 and 1′10-3 s-1 by constant strain rate tests and incremental strain rate tests. Depending on the plots of true stress-true strain and the data of activation energy calculated in the tests, the mechanism of superplasticity was discussed. Results show that for the Ti-48Al-2.3Cr-0.2Mo alloy, there is almost no constant stress stage but hardening is observed in the plots of true stress-true strain. Particularly, at the temperatures above 1025 oC or strain rates below 5′10-4 s-1, a continuous strain hardening stage is observed, and with the increasing of the temperature and the decreasing of the strain rate, the stage increases. High-density dislocation caused by pre-deformation is suggested the reason of hardening. At temperatures from 800 to 900oC, the maximum strain rate sensitivity (m) values are 0.52~0.67, and the activation energy of the alloy is calculated as Qapp =178 kJ/mol, indicating that the dominant mechanism of superplastic deformation is grain boundary siding controlled by grain boundary diffusion. At temperatures from 950 to 1100 oC, the maximum strain rate sensitivity (m) values are 0.63~0.77, and the activation energy of the alloy is calculated as Qapp =290 kJ/mol, suggesting that the dominant mechanism of superplastic deformation is grain boundary siding controlled by lattice diffusion.