The effect of In and Be on the mechanical properties and precipitation behavior of an Al-Cu-Li alloy, which has applications in aerospace and aircraft, has been studied using hardness and tensile tests, differential scanning calorimetry (DSC), and transmission electron microscopy(TEM). The formation of GP zones and delta' phases was retarded, but the T-1 and theta' phases formation were promoted by the addition of In to Al-Cu-Li alloy. However the formation of T-1 and theta' phases, as well as the formation of GP zones and delta' phases, were accelerated by the combined addition of In and Be to Al-Cu-Li alloy. The additional precipitation of T-1 phases which was formed at 160degreesC for a long aging time, was a main reason for the secondary peaks of hardness and tensile strength in Al-Cu-Li alloys added Be and In, or In. The Al-Cu-Li-In-Be alloy was suggested as a material of good combination of tensile strength, elongation and toughness.