The temperature dependence of tensile properties of a two-phase titanium aluminide with nearly lamellar microstructure has been investigated and brittle-to-ductile transition (BDT) temperatures (T-BDS) have been determined under different strain rates from 10(-5) to 10(-1) s(-1). It is found that T-BD rises with the increase of strain rate. From the positive strain rate sensitivity of T-BD, the apparent activation energy of BDT is determined to be 324 kJ/mol by means of Zener-Hollomon factor. The determined activation energy approximates to the activation energies of self-diffusion of Ti atoms, and inter-diffusion of Ti and Al atoms in TiAl phase. The approximation, fractography analysis and theoretical calculation using the Nabarro Model add up to the speculation that the BDT of the alloy is controlled by dislocation climbing.