Friction Stir Welding (FSW) is a solid-state joining process whereby no bulk melting of the base material occurs during joining. FSW avoids severe distortion and formation of as-cast coarse microstructure as well as defects arising from melting and solidification during traditional fusion welding processes. The objective of this investigation is to evaluate the effect of joining parameters on the mechanical and microstructural properties of dissimilar aluminium alloys (3 mm thick AA2024-T3 and AA7075-T6 sheets) joints produced by FSW. Microstructural features have been analysed; while mechanical performance has been investigated in terms of hardness and tensile testing. In both welding configurations the boundary between the base materials at the stir zone is clearly delineated, i.e., no material mixing is observed.