A Mg/Fe-based Layered Double Hydroxide (LDH) intercalated with chloride (Nano iowaite), was synthesized to evaluate its performance for arsenite removal from water. It has a much higher arsenite uptake capacity than other LDHs that are commonly used for water dearsenication. The surface adsorption of the solution arsenite onto the iowaite samples and the anion exchange of the arsenite in solution with chloride, which is originally in the iowaite interlayers, are the primary mechanisms for the uptake of arsenite by iowaite.