The influence of Mn content on the microstructure, tensile properties and strain-hardening behaviors of extruded Mg-1Gd-0.5Zn-xMn (x=0, 0.3 and 1, wt.%) alloy sheets was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The results show that the completely recrystallized grain structure and the extrusion direction (ED)-titling texture are observed in all the extruded sheets. The mean grain size and weakened ED-titling texture of the extruded sheets are gradually reduced with increasing Mn content. This is primarily associated with the formation of new fine α-Mn particles by Mn addition. Tensile properties show that the addition of Mn also leads to the improvement of yield strengths, ultimate tensile strengths and elongations of the extruded Mg-1Gd-0.5Zn-xMn sheets, which is mainly due to the fine grains and α-Mn particles. In addition, the Mg-1Gd-0.5Zn-1Mn sheet has the lowest strain-hardening exponent and the best hardening capacity among all prepared Mg-1Gd-0.5Zn-xMn sheets.