The T-joint is a common joint type frequently used in transport industries because of the importance of increasing the inertia and strength of thin skins and shells without significant weight increase. This shape can be obtained by different processes as extruding, riveting, welding or others. However, the low weldability of some aluminum alloys, when using traditional welding processes, is an obstacle to the possible full benefit of such reinforced structures. The friction stir welding (FSW) process is suitable to join most aluminum alloys and should be considered as a feasible alternative to the other processes used to produce this type of geometry. This paper reports the results obtained concerning FSW T-joints with a new configuration. These joints simulate a typical reinforcement composed by two materials in order to optimize the damage tolerance. The skin is made of a 6xxx series alloy, and the reinforcement is made of a 7xxx series alloy. Mechanical properties were obtained and micro-structural analyses of the weld zone were performed, and the results were compared with those obtained in base materials and butt joints.