The heat treatable aluminum alloy AA2024 is used extensively in the aircraft industry because of its high strength to weight ratio and good ductility. AA6061-T6 aluminum alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength to weight ratio and good corrosion resistance. In the present investigation, the high strength AA2024 and medium strength 6061-T6 were welded by the FSW process, to accertain the optimal mechanical properties by varying the rotational speed from 800 to 1200 rpm and welding speed between 20 to 80 mm/min. This work was aimed at studying the effect of advancing side materials on tensile. Microstructure and micro hardness properties in dissimilar aluminum alloy joints. The experimental results revealed that sound defect-free joints could be obtained when the high strength AA2024 was fixed at the advancing side. The tensile strength was improved at high heat input. The microstructure at AA2024 (Advancing side) shows elongated particles of Al2Cu and MgSi in a matrix of aluminum solid solution and voids were also observed in a matrix.