Effects of aging treatment on the microstructural evolution of a rapidly solidified Al-Li-Cu alloy were investigated by diffcerential scanning calorimetry (DSC) and transmission electron microscopy(TEM). It was found that the precipitation sequence was : supersaturated solid solution α`→metastable δ`+stable precipitate T₁→stable precipitates δ+T₁. Two exothermic and two endothermic peaks are detected by DSC analysis. The two exothermic and endothermic peaks corresponded to δ` and δ+T₁ 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 80KJ/㏖ and the energy for dissolution was 93KJ/㏖. These values are higher than those of Al-Li binary alloy. Peak hardness value (Hv 170) was obtained at 210℃ for 1hr aging treatment which coincided with finishing point of δ` precipitation.