The mechanical properties and fracture behaviors of 6061 aluminum alloy were investigated by the tensile shear tests and in-situ tensile shear tests with tensile shear specimen devised. The results indicate that many slip bands parallel to tensile direction are produced on the surfaces of the specimens. With shear strain rates increasing, the shear yield stress and shear ultimate stress of 6061 aluminum alloy remain constant basically, but the shear fracture strain decreases obviously. The shear strain rates have no influence on the fracture surfaces. The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries parallel to tensile direction under shear stress. With the shear stress increasing, the microcracks extend and coalesce. The fracture of specimens is due to coalescence or shearing between the microcracks. The mechanical properties and fracture behaviors of 6061 aluminum alloy were investigated by the tensile shear tests and in-situ tensile shear tests with tensile shear specimen devised. The results said that many slip bands parallel to tensile direction are produced on the surfaces of the specimens. With shear strain rates increasing, the shear yield stress and shear ultimate stress of 6061 aluminum alloy are constant substantially, but the shear strain rates have obviously no influence on the fracture surfaces. the weakest area and microcracks of the grain boundary parallel to tensile direction under shear stress. With the shear stress increasing, the microcracks extend and coalesce. The fracture of specimens is due to coalescence or shearing between the microcracks.