In order to investigate the effect of erbium (Er) on the microstructure of orthorhombic Ti2AlNb-based alloys, four testing alloys were prepared by adding different contents of the rare earth metal Er to Ti-22Al-25Nb alloy and optical microscopy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, energy-dispersive spectrometry, and transmission electron microscopy were used. The results show that the addition of Er is capable of grain refining and the refinement effect is more obvious with increasing content of Er. The Er2O3 dispersoids formed by internal oxidation and Al3Er compound particles are observed in Er-doped alloys and the number of Er precipitates is increased with increasing Er addition. It is likely that the solubility of Er in the Ti2AlNb alloy is very low and Er precipitates tend to segregate at grain boundaries, which together with the surface activity of rare earth elements is supposed to decrease the prior B2 grain size of Ti-22Al-25Nb alloy effectively. In order to investigate the effect of erbium (Er) on the microstructure of orthorhombic Ti2AlNb-based alloys, four testing alloys were prepared by adding different contents of the rare earth metal Er to Ti-22Al-25Nb alloy and optical microscopy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, energy-dispersive spectrometry, and transmission electron microscopy were used. The results show that the addition of Er is capable of grain refining and the refinement effect is more obvious with increasing content of Er. The Er2O3 dispersoids formed by internal oxidation and Al3Er compound particles are observed in Er-doped alloys and the number of Er precipitates is increased with increasing Er addition. It is likely that the solubility of Er in the Ti2AlNb alloy is very low and Er precipitates tend to segregate at grain boundaries, which together with the surface activity of rare earth elements is supposed to decrease the prior B2 grain size of Ti-22Al-25Nb alloy effectively