Ti-6Al-4V titanium alloy and 5A06 aluminum alloy were successfully butt-joined by friction-stir welding method utilizing a special design of butt-joint configuration. The tool-pin was bias placed toward the aluminum butt-side, accompanying with an excess plunge value of tool shoulder into the top surface of aluminum sheet. The as-welded interface characteristics, joining mechanisms and tensile properties of the modified titanium/aluminum dissimilar butt-joint were performed. Experimental results indicated that the defect-free butt-joints with good formation quality were obtainable when the rotation speed of 1200 r/min, the travel speed of 60 mm/min and the pin offset of 0.5 mm were tailored. The stir nugget zone in joints exhibited a composite-like structure of titanium-alloy particles distributed in aluminum-alloy matrix, with an obvious so-called onion-ring morphology. The energy-dispersive X-ray spectroscopy detections showed that no bulky intermetallic compounds were formed at the titanium/aluminum as-welded interface. The maximum tensile strength of the joint was 265 MPa, which generally reached 84.13% of that of the parent 5A06 aluminum alloy.