The effects of Zn addition on the microstructure and mechanical properties of Mg-10Gd-3Y-0.6Zr (wt.%)alloys in the as-cast, solution-treated, and peak-aged conditions were investigated. Experimental results reveal that the microstructure of the as-cast alloy without Zn consists of α-Mg and Mg 24 (Gd,Y) 5 phases, and the alloy with 0.5 wt.% Zn consists of α-Mg, (Mg,Zn) 3 (Gd,Y)and Mg 24 (Gd,Y,Zn) 5 phases. With the addition of Zn increasing to 1 wt.%, the Mg 24 (Gd,Y,Zn) 5 phase disappears and some needle-like stacking faults distribute along the grain boundaries. Moreover, the 18R long-period stacking ordered (LPSO)phase is observed in the as-cast alloy with 2 wt.% Zn. After solution treatment, the Mg 24 (Gd,Y) 5 and Mg 24 (Gd,Y,Zn) 5 eutectic phases are completely dissolved, and the (Mg,Zn) 3 (Gd,Y)phase, needle-like stacking faults and 18R LPSO phase all transform into 14H LPSO phase. Both the suitable volume fraction of 14H LPSO phases and the fine ellipsoidal-shaped β′ phases make the peak-aged alloy with 0.5 wt.% Zn exhibit excellent comprehensive mechanical properties and the UTS, YS and elongation are 338 MPa, 201 MPa and 6.8%, respectively.