Friction stir welding (FSW) is proved as a promising welding technology for joining dissimilar aluminium alloys. Aluminium alloys are used extensively within the aerospace industry for applications such as fuselage and wing skin panels due to their high strength to weight ratio. Therefore, an attempt is made to optimize the process parameters of friction stir welding using AA2024 and AA6061 age hardenable aluminum alloys in order to improve the tensile properties such as ultimate tensile strength (UTS) and tensile elongation (TE). A response surface method (RSM) based fuzzy grey relational approach (Fuzzy - GRA) is applied using four factors with three levels. The process parameters namely rotational speed (N), welding speed (F), axial load (P) and pin shape (PS). The results indicate a RSM based fuzzy grey relational approach improving tensile properties of FS welded AA2024 and AA6061 aluminum alloys when comparing to conventional grey relational approach. A quadratic relationship was also established between the process parameters and fuzzy grey relational grade.