TiAl alloys are highly promising for high temperature structural application due to their excellent mechanical properties. However, the widespread applications of TiAl alloys have been limited for their low temperature brittleness and poor workability. The further thermo-mechanical treatments is applied for fine microstructures and improved ductility to promote the commercial applications, during which the investigations of hot deformation behavior and microstructural evolution are necessary for the improved microstructure and mechanical properties. The canned forging and subsequent heat treatments of Ti-43Al-4Nb-1.5Mo alloy have been conducted, during which the hot deformation behavior, flow softening mechanism, microstructure evolution and mechanical properties were investigated. The results show that the flow softening process of the canned forging TiAl alloy can be attributed to the soft β phase, α₂/γ lamellae decomposition and the dynamic recrystallization induced by dislocation slipping and twinning in γ phase, and the final microstructure is composed of remnant α₂/γ lamellae and equiaxed α₂, γ and B2 phases. With the increasing heat treatment temperature, the microstructure changes from the multi-phase structure (remnant α₂/γ lamellar, equiaxed α₂, γ and B2 phases) at 1250 ℃ to the α₂/γ lamellar and γ phase at 1285 ℃, and then the fully α₂/γ lamellar structure at 1300 ℃, during which the B2 phase is gradually dissolved due to the solution diffusion, and the remnant α₂/γ lamellae change to equiaxed α₂/γ colonies according to the α₂/γ→γ+α₂+B2 transition, and the final fully α₂/γ lamellar structure is promoted by γ→α transition at high temperature. Moreover, the tensile tests of the hot isostatic pressed (HIPed) samples, canned forged and heat treated samples at 800 ℃ are conducted, in which the fully lamellar structure shows the high properties with the ultimate strength of 663 MPa and the elongation of 26%. The deformation process of the fully α₂/γ lamellar can be strengthened by the lamellae twisting, microvoid inhibition and wavy growth of the cracks, leading to the optimal high temperature performance. Moreover, the disordered bcc β phase can promote the deformation during the hot working process at the high temperature (≥1200 ℃), while the hard-brittle B2 phase severely deteriorates the service properties, which should be controlled accurately for the high mechanical properties during the thermo-mechanical processing.