The residual stresses in gamma phase and alpha(2) phase of duplex microstructures of a two-phase TiAl-based alloy were determined by XRD method; the corresponding macroscopic mechanical properties, such as yield strength, tensile elongation and fracture toughness, were obtained by conventional mechanical tests. From these results, the relationship between the residual stresses and the macroscopic properties were studied and discussed. It was found that the residual stresses have an important effect on the mechanical properties of the alloy, and the possible explanations of this closed relationship were proposed.