<p>The effects of pre-compression and pre-aging on the age-hardening response and microstructure of Mg-9.8Sn-3.0Zn (wt.%) alloy have been investigated via hardness test and advanced electron microscopy. The alloy subjected to both pre-compression and pre-aging exhibits the most refined and densest distribution of precipitates upon aging at 200 °C, leading to the superior age-hardening performance observed in the alloy. Comparatively, the alloy that underwent only pre-aging displayed a greater number density of precipitates than its counterpart that was neither pre-compressed nor pre-aged when both were aged to their peak conditions at 200 °C, indicating an enhanced age-hardening response in the pre-aged alloy. The precipitates in these three peak-aged alloys consist of Mg₂Sn and MgZn₂ phases. The reason why the pre-aged alloy has a higher number density of precipitates than the directly aged alloy is that MgZn₂ phase formed during pre-aging can serve as heterogeneous nucleation site for the formation of Mg₂Sn. The reason why the pre-compression and pre-aged alloy has the highest number density of precipitates is that Mg₃Sn and MgZn₂ phases formed during pre-aging, alongside lattice defects introduced during pre-compression, collectively act as effective heterogeneous nucleation sites for the formation of Mg₂Sn during the subsequent aging at 200 °C.</p>