The mechanism of external sulfate attack (ESA) involves chemical, physical and mechanical processes.Furthermore, ESA is mostly studied on saturated matured sample.However, most concrete structures are exposed to sulfate ingress at early age.This paper describes a comparative study focused on the effect of water curing on the resistance of a Portland cement paste to external sulfate attack.In this study, paste samples prepared with CEM I (Portland cement) at a water to cement mass ratio of 0.6 are immersed in sodium sulfate solution (15 g/l Na2SO4) at controlled pH condition (pH =8±1) after either 24 hours or 1 year of water curing.Sulfate ingress is measured using ICP-AES.The pore distribution is investigated using MIP.SEM images are shown to illustrate the microstructure changes.Our results show that, although sulfate ingress and binding are similar for early age exposure and for matured samples, expansion and cracking fundamentally differ.