Abstract The effects of thermal cycling on the mechanical properties and microstructure of a TiAl-based alloy (Ti46Al8Nb1B) have been investigated for samples with and without an imposed external stress. The temperature range (300–800 °C) and stress (0 or 300 MPa) were chosen to reflect likely industrial usage. Unstressed samples showed no significant effect of thermal cycling. Thermal cycling with external stress is found to reduce the yield stress, ductility and UTS and to increase the amount of primary creep. The microstructural changes include dislocation and twin generation, α 2 /γ ledge formation, dissolution of α 2 lamellae and microcrack formation. The changes in mechanical properties are interpreted in terms of the changes in microstructure.