Abstract: A novel zero-weld-thinning (ZWT) friction stir welding (FSW) process was successfully developed, which can fundamentally eliminate the reduction of weld thickness commonly appeared in conventional FSW. The high-quality ZWT-FSW joints of aluminum alloys can be obtained at low cost and high efficiency without any addition or reduction treatment of base material before or after welding. The results indicated that the strength factor of 97% and the elongation factor of 100% can be obtained during the tensile test of ZWT-FSW joints. Additionally, an increase in the homogeneity of microstructures and mechanical properties can be achieved in weld thickness direction because shoulder effect on base material during FSW was weakened.