Weld fatigue evaluation using the mesh-insensitive Battelle structural stress method has been applied to fusion welds, resistance spot welds and non-welded components. The effectiveness of the Battelle structural stress procedure has been demonstrated in a series of earlier publications for welded structures with different joint types, plate thicknesses, and loading modes. In this paper, a weld fatigue evaluation procedure using the Battelle structural stress method is proposed for friction stir welds currently being used in the automotive and aerospace industries.The applicability of the Battelle structural stress procedure is demonstrated by comparing fatigue life predictions for friction stir welded specimens to well-documented test data from the literature. Different specimen types, plate thicknesses and loading ratios were analyzed for several aluminum alloys.Based on this investigation, a FE based fatigue evaluation procedure for fiction stir welds is established and a master S-N design curve for friction stir welds is constructed. As anticipated the master S-N design curve based on the equivalent structural stress range consolidates the test data with a small scatter band regardless of specimen type and thickness. However, this consolidation clearly shows a load ratio effect. Other fatigue important characteristics of friction stir welds of aluminum alloy are discussed.