Abstract: Natural aging of 2.5 mm thick 7050-T7451 aluminum alloy friction stir welded joints was conducted for 72 h and 17 520 h,respectively. The tensile test,Vickers microhardness test and microstructure observation on the joints were carried out to investigate the effect of natural aging time on the mechanical properties,microhardness profile,microstructure and precipitation. The results show that the yield strength,tensile strength and elongation of the joint subjected to 17 520 h natural aging were about 20%,12% and 25% higher than those of joint natural aged for 72 h. Moreover,the microhardness values were 60 MPa higher in the nugget zone and thermal-mechanical-affected zone in the joint natural aged for 17 520 h. More GP zone,η' and η phases emerged in nugget zone and thermal-mechanical affected zone with increasing the natural aging time,which effectively pinned the dislocations and consequently enhanced the strength and plasticity of the joint.