We have calculated the generalized stacking fault energies including the unstable stacking fault energy (γ us ) and the cleavage energy (γ cl ) at the clean and the oxygen-doped TiAl/Ti 3 Al interface using a first-principles method in order to investigate the mechanical properties of the interface. The [011¯](111) slip system exhibits the lowest γ us and the largest γ cl /γ us among the selected four typical slip systems, showing that the shear deformation in this slip system is energetically favored. Oxygen at the TiAl/Ti 3 Al interface increases the stacking fault energies, and reduces γ cl /γ us for all the selected slip systems, suggesting the presence of oxygen reduce the ductility of the binary phase TiAl-Ti 3 Al alloy.