A combination of transmission electron microscopy and scanning electron microscopy was used to study deformation and fracture behavior of Ti-55531 alloy with bimodal microstructure (donated by BM Ti-55531 alloy) during tensile and torsion tests at room temperature. Results indicate that loading modes have a significant influence on deformation and fracture failure of BM Ti-55531 alloy. First of all, the tension strength is more about 300 MPa than torsion strength of BM Ti-55531 alloy, and its ductilty of tension is also higher. BM Ti-55531 alloy is more sensitive to tensile stress than torsion shear stress.Secondly, deformation mechanism of both tensile and torsion test are a mix mode which combines dislocation slip and shear, while deformation of torsion test was predominantly controlled by shear. These interfaces between net-like grain boundary α, primary α and retained β phases were easly filled with high density dislocations.Thirdly, fractographs of tensile and torsion tested specimens seem to possess different morphologies. Fractographs of tensile specimens are cliffier than torsion specimens. The tensile sample shows a ductile failure, including microvoid coalescence and inter-granular fracture mechanisms. The fracture of torsion specimen is still a mix mode type but with more shear dimples.