The serrated phenomena of the quasicrystalline phase reinforced Mg–4%Li–6%Zn–1.2%Y alloy after the extrusion, solid solution treatment and aged treatment have been investigated at different temperatures. The result shows that when the temperature is above 100 °C, the serrated phenomenon becomes weak and all the serrated amplitudes are lower than 1 MPa. Among them, the serrated amplitude of samples in aged condition is the lowest and the value is only 0.1–0.2 MPa. The underneath mechanism for the lower plastic instability at higher temperature (≥100 °C) can be ascribed to the weak pining effect of solute atoms on the movement of dislocation and release of the pile-up dislocations.