In-situ straining experiments in the TEM have been performed on thin foils of polysynthetically twinned(PST) crystals of Ti-49.3 at% Al. As expected, the deformation behavior of PST crystals of TiAl is anisotropic, depending on the angle between the lamellar boundaries and tensile loading axis. Shear deformation proceeds, in a zigzag fashion, across the lamellar boundaries when tensile loading axis is parallel to the lamellar boundaries. For tensile loading perpendicular to the lamellar boundaries, deformation occurs across the lamellar boundaries, whereas crack propagates along the lamellar boundaries. When tensile loading axis is inclined at an intermediate angle to the lamellar boundaries, shear deformation occurs parallel to the lamellar boundaries. The α₂ phase plays different roles depending on the orientation. Roles of the various types of interfaces in the locallized deformation and fracture behavior have been evaluated to understand the overall behavior of the PST crystals.