Ordered omega (ωo) phases are considered to be equilibrium phases in high Nb-TiAl alloys at intermediate temperatures. However, most studies have focused on the evolution behaviors of these phases during annealing, while the precipitation behavior has not been systematically studied. In the present work, the precipitation behavior of the ωo phase (B82 structure) in the Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y (at.%) alloy during annealing at 850 °C was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After annealing at 1150 °C for 2 h followed by water quenching, the ωo phase in the as-cast alloy transformed to the βo phase. At the initial stage of annealing processing at 850 °C, the ωo phase re-precipitated at the γ/βo boundaries and the size of the ωo phase increased with the annealing time. Moreover, the γ plates precipitated within the βo phase at this temperature became coarser and tended to globalize during annealing. In addition, the α2 and D88-ω phases were also observed at the γ/βo boundaries. Energy dispersive X-ray spectroscopy (EDS) and Scanning transmission electron microscopy (STEM) analysis showed that the D88-ω phase is rich in W and Nb elements. The corresponding mechanisms of the transformation mentioned above were discussed.