Creep tests of high Nb containing TiAl alloy were carried out at different temperatures and various stresses, combining with scanning electron microscope (SEM), transmission electron microscope(TEM) and other analytical methods, the effect of nano Y₂O₃ on high temperature creep performance of Ti-45Al-6Nb-2.5V alloy was explored. The microstructure of the as-cast high Nb containing TiAl alloy consists of α₂/γ lamellar feature. In addition, the microstructure was refined significantly and the high temperature tensile properties were improved with the addition of Y₂O₃. According to results from creep tests, the creep resistance of Ti-45Al-6Nb-2.5V alloy is considerably improved after adding 0.15at.% nano Y₂O₃, the steady-state creep rate at 800℃/300MPa decreases from 2.389×10^_-7s^_-1 to 1.500×10^_-7s^_-1; and the creep life of Ti-45Al-6Nb-2.5V alloy at 850℃/250MPa increases from 14.10h to 61.50h. The mechanism of adding nano Y₂O₃ to improve creep resistance is that Y₂O₃ has high bonding strength with the matrix, which can effectively hinder the movement of dislocations and weaken the tendency of cavities to initiate. After analysis, the creep behaviors of the two alloys at 800℃/300MPa are mainly controlled by dislocation climbing and twinning, and the creep damage and fracture mechanism is initiation of voids and propagation of cracks.