In this study, effects of different operating conditions on friction stir welding (FSW) of dissimilar sheets of 5050 aluminum (Al) alloy and 304 stainless steel have been investigated. Recently, FSW process has been used for joining of dissimilar materials due to its ability to eliminate local casting defects of the conventional fusion welding techniques. Microstructure and mechanical properties of weld nugget in FSW process mainly depend on several parameters such as tool rotational speed, feed rate, offset, and pin profile. In the present work, effects of tool rotational speed, feed rate and offset, together with annealing process on the tensile behavior and microhardness of the welding procedure were investigated and discussed. Based on the experiments, our results showed that decreasing tool rotational speed from 710 to 500 rpm besides increasing tool feed rate from 40 to 80 mm/min leads to an improved joint. Furthermore, the defect on the stirred zone was decreased by increasing the tool offset up to 1.5 mm. On the other hand, enhancements of up to 100 and 9 % in elongation and tensile strength were achieved by applying the annealing process, respectively.