The process of joining light weight materials is highly essential and difficult task in the manufacturing industries. This paper presents one of the joining processes of light weight alloy which is Friction stir welding (FSW). It is solid state material joining method and a promising technique for non ferrous alloys. The present work is an attempt made to study the significant effects of tool parameters such as shoulder diameter of the tool, tool offset (distance from the weld center) and tool tilt angle on the tensile properties (ultimate tensile strength, yield strength and % elongation) of the dissimilar friction stir welded aluminium 5083-H111 and 6082-T6 alloys. Twenty number of experiments were conducted based on design of experiments (DOE) using central composite design technique. The mathematical model is developed to predict the tensile properties of the joint and ANOVA test is performed to check the model adequacy. Further Response surface methodology is applied to study the effect of tool parameters on the tensile properties. The highest tensile properties were observed at shoulder diameter of 18 mm, 0 mm tool offset and 1° tool tilt angle without any defects. Microstructure studies by SEM and EDAX analysis of the joints revealed that no formation of intermetallic compounds and tunnel defects are reported for the samples which show high tensile properties.