Effect of aging treatment on the microstructural evolution of a rapidly solidified Al-3.56wt%Li-0. 97wt%Mg alloy were investigated by differential scanning calorimetry(DSC) and transmission electron microscopy(TEM). DSC analysis showed two exothermic and two endothermic peaks. The two exothermic and endothermic peaks corresponded to δ′and δ＋T precipitation and dissolution reactions respectively. The enthalpy of δ´precipitation decreased with increasing of aging temperature and time until the finishing point of precipitation. The activation energy for precipitation of δ´ was measured as 78KJ/㏖ and the energy for dissolution was 95KJ/㏖. These values are higher than those of Al-Li binary alloy. Peak hardness value(Hv 155) was obtained at 210℃ for 1hr aging treatment which coincided with finishing point of δ´precipitation.