Fracture behavior of fully lamellar (FL) and duplex phase (DP) TiAl alloys is reported in this paper. It was found that the inverse behavior of coarse FL TiAl alloy showing inferior tensile properties but superior fracture toughness resulted from the different fracture mechanisms of these two types’ tests. In tensile specimens, the final fracture happened at a section that was most heavily damaged by the accumulation of large interlamellar microcracks and arbitrarily located within the gauge-limited volume. In 3PB notch specimens, the propagation of the main crack was constrained within a narrow strip nearby the centerline where the normal stress was the highest. Large lamellar grains caused serious damage in tensile tested specimens. However multi-oriented large lamellar grains formed seriously bifurcated crack tips, which made the crack propagation more difficult in 3PB notched specimen. The main mechanisms of toughening in FL specimens were the deflection of main crack, bifurcation and blunting of crack tip and formation of a diffuse zone of microcracks. These phenomena reduced the driving force for crack extending and then increased the fracture toughness.