Magnesium rare earth alloys have been received extensive attention due to their attractive mechanical properties. The precipitation sequence in laser welded Mg–3Nd–0·2Zn–0·4Zr (NZ30K) alloy during aging treatment has been investigated using transmission electron microscopy (TEM). The results show that the tensile strength of laser welded NZ30K can be improved significantly after aging treatment at 200°C for 8 h. The precipitation in laser welded NZ30K alloy follows the sequence of super saturated solid solution→ β″(DO19)→ β′(fcc)→ β. The results of incremental of critical shear stress component are Δ τs/Δ τp/Δ τr/Δ τf = 1·86∶3·57∶3·14∶1. The platelet of precipitates with high volume fraction is the most important factor that enhances aging treatment strengthening.