The addition of calcium (Ca) simultaneously improves the ductility and strength of UFG Au wires. Based on the observation on stacking faults, microstructures, simulation results and significant effect of Ca on grain boundary related properties, it is inferred that segregation of Ca to stacking faults and grain boundaries has occurred to induce effective stacking fault energy (SFE) reduction and properties improvement. Considering the known greater impact of SFE in UFG/ NC metals, segregating dopants are proposed to be an effective strategy for achieving dual improvement in this class of materials. Also, dopant selection criteria for this purpose is also suggested and verified.