By means of in-situ tensile test of the specimen of bi-morphic alloys of γ-TiAl,observation upon its corresponding fracture surface with scanning electron microscope, and finite element computation, the tensile fracture mechanism of these alloys is investigated. The results reveal that most cracks are initiated and propagated along the interfaces between lamellae before the starting of plastic deformation. The driving force of fracture process is the tensile stress. In specimens with a slit notch, most cracks are initiated directly from the notch root and extend along lamellar interfaces. The main crack and a new one are then linked by the translamellar cleavage fracture over the barrier grain when the applied load increases. In V-notch specimens, however, a crack may be initiated at a distance in front of the notch root. The FEM calculations reveal that the fracture strength along lamellar interfaces (interlamellar fracture) is as low as 110 MPa and appreciably lower than that along the interfaces perpendicular to the lamellae (translamellar fracture), which shows a value higher than 250 MPa. This explains the reason why cracks nucleate and extend preferably along the lamellar interfaces.