In this study, dissimilar friction stir welding (FSW) processes were performed using Taguchi L9 orthogonal layout on AA 5083 H111 and AA 2024 T351 plates. The ultimate tensile strength (UTS) and percentage of elongation (epsilon(1)) were evaluated as the performance characteristics of the FS welded joints. A Taguchi based grey relational analysis was conducted using a grey relational grade (GRG) to obtain a welded joint with an optimal combination of high strength and ductility. Taking the largest mean value of GRG into consideration, the optimal welding combination was obtained using a tool with straight-threaded pin shape with the process parameters of 500 min(-1) tool rotational speed (TRS) and 63 mm/min welding speed (WS). This combination was obtained from the experimental combinations in the Taguchi L9 orthogonal layout. Additionally, analysis of variance was performed to investigate the effect of parameters on GRG value and significance of the parameters. It was revealed that the effectiveness of each parameter was ranked: TRS (48.02 %) > tool type (30.60 %) > WS (21.12 %). Tunnel and cavity-type defects were found to occur in the welded joints produced with the TRS of 630 and 800 min(-1). Notably, the weakest welded joints were produced with the WS of 63 mm/min and 80 mm/min.