Abstract: H70 brass plates with 2-mm-thick were successfully joined by cold source assisted friction stir welding. The microstructure and mechanical properties of the welded joint were investigated by optical microscopy, scanning/transmission electron microscopy, electron backscatter diffraction, microhardness measurement and tensile tests. The obtained results showed that significant reduced peak temperature and increased cooling rate were achieved by using liquid nitrogen cooling. The stir zone showed the ultra-refined grain structure with high dislocation density. The crystallographic shear texture whose dominant component of -1 1 2<1 1 0> was also found. The heat-affected zone disappeared as well. As a result, the ultimate tensile strength was enhanced by 58% compared with that of the base metal without ductility loss. A good strength-ductility synergy achieved by using cold source assisted friction stir welding technology.