Abstract: The microstructure and mechanical properties of high Nb-TiAl alloy exposed to isothermal aging at 850 ℃processing were investigated using optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer(XRD) and microhardness and other testing methods.The results indicate that the microstructure of the as-forged high Nb-TiAl alloy is a near-laminated structure with jagged grain boundary, the sheet mass size is about 112 μm, and the interlamellar spacing is about 1.6 μm.The microstructure of the alloy is mainly composed of γ phase and α₂ phase.During an 850℃isothermal period of 5 min, 5 h, 10 h, 20 h, respectively, the microstructure mainly consists of lamellar structures formed by γ phase, α₂ phase and a small amount of β phase during the high-temperature aging.With the extended isothermal time, both the alloy sheet layer group and the sheet layer spacing have obvious coarsening phenomenon.In different isothermal time time, the surface of the alloy shows a relatively high hardness value (420-460 HV), and its microhardness decreases with the extension of the insulation time.