A study was conducted to examine the precipitation phenomena of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry and transmission electron microscopy. DSC curves were measured over the temperature range of $25{sim}550^{circ}C$ at a heating rate of $2{sim}20^{circ}C$/min.. Three heat evolution peaks and three heat absorption peaks were observed in the DSC curve for the as-quenched specimen. From DSC results and TEM analysis, it was proved that the precipitation sequence in the as-quenched specimen is supersaturated solid solution ${ ightarrow}$ GP zone ${ ightarrow}{delta}^{prime}{ ightarrow}T_1{ ightarrow}T_2$ and ${ heta}^{prime}$ was detected in the peak aged specimen at $160^{circ}C$. The major phase formed at peak hardeness in the aging at $160^{circ}C$ was ${delta}^{prime}$ phase. The activation energies for the formation of ${delta}^{prime}$ and $T_1$ phases were 22.3kcal/mole and 24.3kcal/mole, respectively. These lower activation energies than those for diffusion of Cu and Li in Al are ascribed to the quenched-in excess vacancies.