Friction stir welding (FSW) is a solid-state joining technique which can produce high-quality joints efficiently. The residual stresses in FSW are generated due to the effect of both the uneven temperature field and of the tool force, which is different from that in fusion welding. In this study the residual stresses of 3mm-thick 2024-T4 aluminum alloy FSW joints have been investigated by using the Hole-drilling method. To reduce the influence of drilling upon the experimental results, annealed stress-free 2024 aluminum alloy plates were drilled; the relieved strains were measured and were subtracted from the total strains measured from the joints. The results showed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses; high longitudinal tensile residual stresses were concentrated near the tool shoulder direct affected zone and asymmetrically distributed at the different sides of the weld line; i-e, high at the advancing side and relatively low at the retreating side. Outside the tool shoulder direct affected zone, the longitudinal residual stresses decreased rapidly and became compressive residual stresses away from the weld line; the peak of the longitudinal residual stresses was 164.5MPa.The mechanism of the generation of the residual stresses was analyzed preliminarily.