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In this study, the ultrafine-grained (UFG) Cu–5Mn alloys were prepared by friction stir processing (FSP) to investigate the influence of short-range ordering (SRO) on the tensile deformation behavior. Due to the dynamic recrystallization, the uniform and equiaxed UFG microstructures were obtained in FSP Cu–5Mn alloys with low density of dislocations, high fraction of high-angle grain boundaries, high Taylor factor and high degree of recrystallization. The introduction of Mn atoms into the Cu matrix cannot change the stacking fault energy apparently but increase the SRO degree. Although the dominant mechanism was still the wavy slip of dislocation, the planar slip of dislocations was motivated and many twin layers were observed in the ultrafine grains of FSP Cu–5Mn alloy. The change of SRO degree can significantly improve the dislocation storage capacity during the tensile deformation process, and promote the improvement of the strain-hardening rate, resulting in an excellent strength-ductility match in FSP UFG Cu–5Mn alloy.