Effects of aging treatment on the microstructural evolution of a rapidly solidified Al-Li-Cu alloy were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy(TEM). It was found that the precipitation sequence was: supersaturated solid solution ${alpha}^{prime}$ ${ ightarrow}$ metastable ${delta}^{prime}$ + stable precipitate $T_1$ ${ ightarrow}$ stable precipitates ${delta}+T_1$. Two exothermic and two endothermic peaks are detected by DSC analysis. The two exothermic and endothermic peaks corresponded to ${delta}^{prime}$ and ${delta}+T_1$ precipitation and dissolution reactions respectively. The enthalpy of ${delta}^{prime}$ precipitation decreased with increasing of aging temperature and time until the finishing point of precipitation. The activation energy for precipitation of ${delta}^{prime}$ was measured as 80KJ/mol and the energy for dissolution was 93KJ/mol. These values arc higher than those of AI-Li binary alloy. Peak hardness value (Hv 170) was obtamed at $210^{circ}C$ for 1hr aging treatment which coincided with finishing point of ${delta}^{prime}$ precipitation.