•Plastic deformation behavior of α-Mn single crystals was investigated by micropillar compression at room temperature.•α-Mn single crystals are found to plastically deform by dislocation motion at room temperature, accompanied by very high yield stresses of the range of 4–6 GPa.•Slip along 111 and 001 are identified to operate.•Any low-indexed slip planes cannot be assigned for both slip, because of the significantly wavy nature of slip lines. The deformation behavior of single crystals of α-manganese has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. When the specimen size is reduced to the micrometer-range, single crystals of α-manganese are found to plastically deform by dislocation motion at room temperature for the first time, accompanied by very high yield stresses of the range of 4–6 GPa. Slip along 111 and 001 are identified to operate for compression axis orientations near 001 and near 011 and 1¯11, respectively. Any low-indexed planes cannot be designated as the slip plane for both slip along 111 and 001, because of the significantly wavy nature of slip lines caused by the occurrence of frequent cross-slip. Slip along 111 tends to prefer the slip plane of {112} rather than {110}. Slip along 001, on the other hand, tends to occur on the maximum resolved shear stress plane. The 1/2111 dislocation carrying slip along 111 moves as a perfect dislocation without dissociating into partials and does not have any preferred orientation. The 001 dislocation carrying slip along 001 also moves as a perfect dislocation without dissociating into partials. Although the Peierls stress for the motion of these dislocations must be very high, there seems no deep Peierls valleys along particular directions, unlike the screw direction for the 1/2111 dislocation in body-centered cubic metals. Display omitted