Microstructural analysis of a (α + β) Ti alloy was investigated to consider phase transformation in each step of the thermo-mechanical process using by SEM and TEM EDS. The TAF (Ti-6Al-4Fe) alloy was thermo-mechanically treated with solid solution at 880 oC, rolling at 880 oC and annealing at 800 oC. In the STQ state, the TAF microstructure was composed of a normal hcp α and metastable β phase. In a rolled state, it was composed of fine B2 precipitates in an α phase, which had high Fe segregation and a coherent relationship with the β matrix. Finally, in the annealing state, the fine B2 precipitates had disappeared in the α phase and had gone to the boundary of the α and β phase. On the other hand, in a lower rolling temperature of 704 oC, the B2 precipitates were more coarse in both the α and the boundary of α and β phase. We concluded that microstructural change affects the mechanical properties of formability including rolling defects and cracks.