The purpose of this research is to study the durability of porous aggregate concrete against chloride attack by examining the influence of porous aggregates on chloride ion (Cl^-) diffusivity of concrete and Interfacial Transition Zone (ITZ) properties, and to investigate the influence of curing conditions; which are curing temperature and curing period; on Cl^- diffusivity and ITZ properties of concrete using four types of aggregate. Three types of porous aggregates; Japanese artificial lightweight aggregate, coral aggregate and crushed clay brick aggregate; are employed to compare with crushed limestone aggregate. Three different water-cement (W/C) ratios are used in this study. The properties of ITZ around coarse aggregates, such as the thickness and the Cl^- diffusivity of ITZ, are measured and used to explain the influence of porous aggregates and curing conditions on the Cl^- diffusivity of concrete. The results show that Japanese artificial lightweight aggregate concrete has lower Cl^- diffusivity compared with normal aggregate concrete because the Japanese artificial lightweight aggregate has a dense outer crust, thus Cl^- can not penetrate through aggregate and ITZ phase. Coral and brick aggregates, which are poor quality aggregates, have very high water content when they are in saturated surface-dry condition causing a thicker water film around aggregates and Cl^- can easily penetrate through them. Therefore, concrete made from coral and brick aggregates have higher Cl^- diffusivity and show expectedly poor performance under marine environment. Finally, the improvement for the poor quality aggregates by using dry aggregates for mixing concrete is successfully proposed in this study.