Friction Stir (FS) welding promises joints with low porosity, fine microstructures, and low vaporization of volatile elements compared with conventional welding techniques. FS weld was carried out on Vacuum Induction Melted 5 mm thick cast Aluminum-Magnesium-Scandium (Al-Mg-Sc) alloy plates. Microstructural evaluation revealed that due to FS welding, fine and fragmented dynamically recrystallized grains have been formed in the weld nugget. Tensile fracture occurred out side the weld zone. The tensile strength of the welded joint is more than the cast base metal. The hardness of the FS welded joint is less than the hardness of the cast basemetal. The minimumhardnesswas located on the retreating side of the weld. These results clearly show that FSWprocess is amenable to join cast Al-Mg-Sc alloy. © Indian Institute of Metals 2012.