The 7075-T6 aluminum alloy is one of the strongest aluminum alloys that possess excellent combination of mechanical properties such as high strength to weight ratio, good corrosion resistance and thermal conductivity but they generally present low weldability by traditional fusion welding process. Friction stir welding is a new solid state process that is function of different process parameters. In the current study, to investigate the effect of some of the main welding process parameters such as rotational speed, traverse speed and tool shoulder diameter properly, a Design of Experiment (DOE) was used with a Response Surface Methodology (RSM) approach to find the best process settings and achieve optimal performance. Results showed that to achieve sound high-grade joints parameters should be optimized. When improper welding parameters are used, problems such as defect formation, precipitates dissolution and grain growth can deteriorate the mechanical properties of the joint. So, of the twenty joints fabricated using various welding parameters, the joint fabricated at a rotational speed of 1050 rpm, welding speed of 100 mm/min and shoulder diameter of 14 mm exhibited superior metallurgical and mechanical properties in comparison to other fabricated joints.