The early age hardening behavior in Al-Cu-Mg alloys with fixed Cu content (0.50 wt%) and varying amounts of Mg has been studied by hardness tests and TEM observation. Two alloys both exhibit the early rapid hardening phenomenon based on large solute-aggregates analysis. Ageing time of early stage rapid hardening of Al-0.5Cu-1.99Mg alloys is less than that of Al-0.5Cu-1.48Mg alloys. For two alloys, ageing time of early stage rapid age hardening reduces with artificial ageing temperature increasing. The early stage rapid age hardening is depended on the composition and artificial ageing temperature. Forming larger solute-aggregates may give rise to early rapid age hardening.