Differential speed rolling (DSR) has been carried out on AZ31 alloys with Mn additions of 0 to 0.6 wt% for investigating the effects of Mn on microstructure, texture, mechanical properties, and formability. The Al–Mn compounds were formed in the sample with a Mn addition of only 0.2 wt% because of its low solid-solubility limit. There were tiny differences among the DSR-processed AZ31 alloys with different Mn contents, while the AZ31 alloy without Mn addition exhibited a more homogeneous microstructure, a weaker basal texture intensity, and a much superior formability together with a larger likelihood of grain growth during annealing. The Mn dissolving in αMg matrix exerted a far stronger influence on the resulting properties compared with those existing in form of the Al–Mn compounds. The Mn solute atoms induced an increase in c/a ratio, which may suppress activity of nonbasal slips and in turn degrade the deformation capability.