A novel precipitation sequence, super-saturated-solution → stacking faults → Mg3Gd, i.e. S.S.S. → SF → β1, was established for a Mg-3Zn-2Gd (wt%) alloy. Solute pre-precipitation can occur during the solidification of as-cast alloy and subsequent solution-treatment, resulting in the formation of lamella structures with …ABCABC… stacking sequence. The lamella structure will transform to the Mg3Gd phase, even that Mg3Gd is not the most stable phase in this serial alloys.