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Layered double hydroxides (LDHs) with different kinds of metal ions (Mg-Al, Co-Fe, Ni-Fe, and Mg-Fe) in the brucite layers were prepared and their anion exchange properties were studied by measurements of distribution coefficient (K d ) and ion exchange capacity. The basal spacing of LDHs varied depending on the kind of metal ions in the brucite layer. A relatively high K d value for NO 3 2 ions was observed on Ni-Fe type LDHs, and a markedly high K d value for the hydrothermally-treated Ni-Fe type LDHs (Ni-Fe (HT)), prepared at 120 °C. These high K d values correlated with the basal spacing of 0.81 nm observed for this sample, where the interlayer distance (0.33 nm) is suitable for the stable fixing of NO 3 2 ions (ionic size = 0.33 nm). A chemical analysis study showed a Cl 2 /NO 3 2 ion-exchange mechanism for NO 3 2 adsorption on Ni-Fe (HT). The NO 3 2 uptake by Ni-Fe (HT) was nearly constant (NO 3 /Fe = 0.7) over a pH range between 5 and 10, which also supports the adsorption mechanism of Cl 2 /NO 3 2 ion exchange. The Ni-Fe (HT) could remove NO 3 2 ions from seawater effectively (NO 3 2 uptake = 168 mmol g 21 ) even though seawater contains an extremely large amount of coexisting anions. This novel adsorbent thus has a NO 3 2 ion-sieve property and will prove beneficial for the selective removal of NO 3 2 ions from industrial effluents and seawater to clean the environment.