Microstructural evolution and Portevin–Le Chatelier(PLC) phenomenon of the as-extruded Mg–4%Li–6%Zn–1.2%Y alloy before and after heat treatment have been investigated.It has been demonstrated that for the as-extruded and solid solution treated(T4) samples,the PLC phenomenon could be obviously observed on tensile stress–strain curves.Moreover,the PLC phenomenon in T4 samples was more salient than that in the as-extruded condition,suggesting that the occurrence of PLC phenomenon was closely related to the super-saturation degree of solute atoms in the matrix.Since most of solute atoms were consumed for the formation of Mg Zn precipitates(β1′ and a little of β2′) during the subsequent ageing treatment(T6),the PLC phenomenon of T6 samples was eliminated.Meanwhile,due to the pinning effect of the formed Mg Zn precipitates on mobile dislocations,the tensile strength of T6 samples was relatively higher than those of the other two conditions. Microstructural evolution and Portevin-Le Chatelier (PLC) phenomenon of the as-extruded Mg-4% Li-6% Zn-1.2% Y alloy before and after heat treatment have been investigated. It has been been demonstrated that for the as-extruded and PLC solution could be significantly observed on tensile stress-strain curves. Moreover, the PLC phenomenon in T4 samples was more salient than that in as-extruded condition, suggesting that the occurrence of PLC phenomenon was closely related to the super-saturation degree of solute atoms in the matrix. The most most solute atoms were consumed for the formation of Mg Zn precipitates (β1 ’and a little of β2’) during the subsequent aging treatment (T6), the PLC the phenomenon of T6 samples was eliminated. However, due to the pinning effect of the formed Mg Zn precipitates on mobile dislocations, the tensile strength of T6 samples was relatively higher than those of the other two conditions.