Ultrafine-grained (UFG) pure Cu and Cu–Zn alloys samples were prepared using cold-rolling under liquid nitrogen temperature to investigate the influence of stacking fault energy (SFE) on the mechanical properties and microstructure. The tensile tests were performed at room temperature with the strain rate of 10-4/s, and the strain hardening rate (SHR) was computed from the engineering stress-strain curves. A decrease in SFE simultaneously improves strength and ductility. The average grain sizes, microstrain, dislocation density and twin density were examined using X-ray diffraction (XRD). X-ray diffraction measurements indicate that grain size decreased and microstrain, dislocation and twin densities increased with decreasing SFE.