Abstract：By means of creep properties measurement and microstructure observation, an investigation has been made into the microstructure and creep properties of as-cast TiAl-Nb alloy in the temperature ranges of 800--910篊. Results show that the microstructure of as-cast TiAl-Nb alloy consists of r/a2 phases with the lamellar feature. The boundaries with the irregular jagged configuration are located in between the different oriented lamellar phases, and the single r is distributed in the region near the boundaries. The creep lifetime of as-cast TiAl-Nb alloy is measured to be 237 h under the applied stress of 120 MPa at 900 篊, and the creep lifetime of the alloy is measured to be 307 h under the applied stress of 220 MPa at 800篊. The deformation mechanism of alloy during creep is dislocation slipping within the lamellar r/a2 phases, and the boundaries between the lamellar r/a2 phases may hinder dislocation slipping. During steady state creep, the lamellar r/a2 phases in the alloy may be contorted due to the double orientation slipping of dislocations. In the latter stage of the creep, the micro-crack may be initiated and propagated along the grain boundaries being perpendicular or at about 45?angles relative to the stress axis, under the action of maximum shear stress, up to the occurrence of creep fracture, which is thought to be the fracture mechanism of alloy during creep.