Aging and reversion behaviors in both alloys were investigated by means of electric resistivity measurement, X-ray diffraction and high resolution electron microscopy. The resistivity-aging time curves of the alloys quenched from 520°C and aged at various temperatures showed a range in which resistivity is unchanged. The resstivity in this range increased with aging temperatures and saturated to ρ=1.55μΩ•cm at about270°C. The fact means that clusters and G. P. zones can be formed below about 270°C and that the homogeneous solid solution state can be achieved above this temperature. A trace element of Sn in the Al-4% Cu alloy reduced cluster formation and accelerated θ" precipitate formation. Heating preaged alloys at temperatures from the preaging temperature to about 270°C lead to not only disolution and growth of G. P. zones but also new formation of clusters, G. P. zones and θ' and θ" precipitates, which probably resulted in incomplete reversion. G. P. zones in the Sn-containing alloy dissolved more smoothly than in another alloys.