Specimens of a fully lamellar TiAl alloy and a duplex TiAl alloy were tensile tested using load-controlled procedure. The microcracks were measured for each specimen as it was subjected to various preloading-unloading processes. Loading-unloading-reloading processes of in-situ tensile tests were carried out in a scanning electron microscope (SEM). Effects of microcrack damage on the deformation and fracture behavior were evaluated. The following results of microcrack-damage on deformation and fracture behavior of TiAl alloy were found: (1) The apparent plastic elongation resulted mainly from plastic strain. The elongation caused by microcracks is negligible. (2) No appreciable effects of microcrack damage on the apparent elastic modulus could be found. (3) Microcracks damage produced at higher preloading reduced the fracture stress, however, that produced at lower preloading gave diminished effects.