The effect of small addition of Ag, Mg on the microstructure and the aging characteristics of Al-3.5Cu-1.0Li alloy has been studied by mechanical testing and transmission electron microscopy. The results indicate that only sliver addition has almost no effect on the age-hardening and strengthening of the baseline alloy upon aging at 175 ℃. At peak aging state the main precipitates are both coarse T1 and θ′ phases for the Ag-bearing alloy and the baseline alloy. The Mg-containing alloy has a faster aging response and higher aging-strengthening effect than the baseline alloy. GP zone, θ′ and T1 are formed at different aging stages. The combined addition of Ag and Mg to the alloy greatly accelerates T1 precipitation, resulting in increasing density of T1 precipitates. The high volume fraction of T1 phase causes 2050 alloy having the highest strength. The independent and combined roles of small addition of Ag and Mg can be interpreted in terms of the solute-vacancy interaction and solute-solute atom interaction.