Abstract: The fatigue performance of 2524-T3 aluminum alloy base metal and three kinds of size of friction stir welded (FSW)butt joints was studied. The S-N curves of samples were obtained and analyzed. The results show that when the fatigue life was 1×105 cycles, the fatigue strength of FSW butt joint with small thickness and short weld seam was 80.8% of the fatigue strength of base metal, the fatigue strength of the joint with big thickness was 80.3% of the joint with small thickness and short weld seam, and the fatigue strength of FSW butt joint with big weld seam was 79.9% of the joint with small thickness and short weld seam.