Abstract: The present research employed a modified butt joint configuration into the FSW of TC4 titanium alloy and 5A06 aluminum alloy with an excess pin offset setup towards titanium alloy butt side, aiming to reduce the tool shoulder attrition, avoid butt root flaws, and study the effects of the process variables on the weld interfaces and tensile properties. Under the best FSW process condition, the examinations and analyses of macro/micro-structures, mechanical tensile properties of the dissimilar joints were conducted. The experiment results show that the joint mechanical tensile strength can reach 88.3 % of the parent aluminum alloy strength,and the tensile fracture path mainly within the stir nugget zone at aluminum alloy butt side. The formation mechanisms of the Ti/Al butt-welded interface structures were detailed according to the analyses of the characteristics at the butt interface. A high-quality Ti/Al FSW butt joint could be obtained when lower tool rotating speed and lower pin-offset value towards titanium alloy butt side were used.