Abstract: Mg-10Gd-1.5Zn-xMnalloy（x =0.5, 1.0, 1.5, wt%） was prepared. The effects of Mn content on the microstructure and mechanical properties of Mg-10 Gd-1.5 Zn alloy were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and X-ray diffractometey（XRD）. The results show that the α-Mg dendrites of the as-cast Mg-10Gd-1.5 Zn alloy are refined with the increase of Mn content, and the（Mg, Zn）₃ Gd phase changes from continuous irregular strips to intermittent strips or even granulars; Mn encourages the dispersion of Gd and Zn atoms when the content of Mn exceeds 1.5 wt%. The as-cast alloy structure precipitates the 18R-LPSO phase, and the alloy’s yield strength and tensile strength dramatically rise to 103.52 MPa and 141.37 MPa, respectively. These values are 9.35% and 16.7% bigger than those of the Mg-10Gd-1.5 Zn alloy, respectively.