Evolution of grain boundary α (GB α) in a α+β titanium alloy had been examined by morphology and crystallographic orientation analysis. The results indicate that GB α only retains a Burgers orientation relationship (BOR) with one of the adjacent β grains in most of the prior β/β boundaries. The colony α (single crystallographic variant of parallel α plates) tends to evolve in the adjacent β grain that maintains BOR with GB α, whereas the dendritic α (small protuberances of GB α) tends to grow in the other adjacent β grain that does not maintain BOR with GB α. Additionally, two α colonies developing into two adjacent β grains from GB α keep the same crystallographic orientation as that of GB α when GB α maintain a near BOR with both adjacent β grains in a special prior β/β boundary (60°/<110>). These observations are understood from the perspective of minimum interfacial energy and strain energy.