The initial lamellar microstructure of titanium alloys significantly affects their microstructural evolution and mechanical property during thermo-mechanical treatments. Thus, the evolution of the initial lamellar microstructure must be explored to control the microstructure and enhance the mechanical property. The present work focuses on the evolution of the lamellar microstructure during β→α phase transformation via interrupted furnace cooling experiments to analyze the growth behavior of the grain boundary α phase (α_GB) and its effect on the subsequent growth of intragranular α lamellae and microtexture. Results show that when titanium alloy furnace cools from the β phase field to the α + β phase field, the α_GB holding Burgers orientation relationship (BOR) with both sides of β grains (2-BOR α_GB) has an advantage for early transformation at the β grain boundary. In particular, type II (49.5°/<110>) and type III (60°/<110>) β grain boundaries are preferential sites for the early nucleation of α_GB particles. As the temperature decreases, α lamellae holding similar orientation to 2-BOR α_GB grow to both sides of β grains. Thus, 2-BOR α_GB and both sides of α lamellae form a strong microtexture at the grain boundary. At the early growth period of the α phase, the smaller the θ_2-BOR (misorientation of the close-oriented α_GB variant pair of parents β1 and β2) of 2-BOR α_GB, the earlier the formation of a strong microtexture at the grain boundary. 2-BOR α_GB preferentially precipitates, whereas the α_GB holding BOR with only one side of the β grain (1-BOR α_GB) nucleates. α lamellae holding a similar orientation to 1-BOR α_GB grow to one side of the BOR-β grain (holding BOR with α_GB), whereas α lamellae with a different orientation grow in the non-BOR-β grain. Thus, 1-BOR α_GB and one side of α lamellae form a weak microtexture at the grain boundary.