Abstract: Neutron diffraction method was utilized to measure residual stress distribution of friction stir welded 2024-T4 aluminum alloy plates. Residual stress distribution at different zones inside the weld was obtained and effect of welding speed on residual stresses was studied. Results show that longitudinal residual stresses are main residual stresses which are higher than transverse ones. Under the same tool rotating speed, longitudinal residual stresses will increase with the increment of welding speed. Transverse residual stresses are quite small except near the key hole.