Layered double hydroxides (LDHs) for use as anion exchangers were prepared from steelmaking slag discharged by a steel-manufacturing company. Metal elements were leached from the slag with HCl as a source of metal ions. LDHs were synthesized from the slag leachate at various pHs by a co-precipitation method, and their physical and chemical properties including the crystal structure, thermogravimetric properties and chemical composition were investigated. The ability of the products to remove toxic anions was examined for As(III), B, Cr(VI) and Se(IV) in aqueous solution. It was found to be appropriate to leach the slag with 2.0 mol/dm(3) HCl at a solid-liquid ratio of 2.5 g/100 cm(3). The reaction products obtained from slag leachate included Mg-Al and Ca-Al LDHs, of which Mg-Al LDH was predominant at pH 11 and below, while mixtures of Mg-Al and Ca-Al LDHs were mainly formed at pH 12 and above. In synthesizing LDHs from slag, controlling the percentage of Ca precipitated in the slag leachate by adjusting the synthesis pH is an important factor in determining the kind of LDH formed. The LDHs prepared removed toxic anionic species in the order of Cr(VI)>Se(IV)>As(III)>B. In addition, slag LDH containing Fe was found to show better adsorption of As(III) than the standard LDH synthesized from pure reagents. The anion removal of the LDHs synthesized from slag varied remarkably with the synthesis pH, and the product synthesized at pH 10.5 was found to have the highest performance in anion removal. Thus, LDHs with excellent anion removal ability can be prepared from steelmaking slag.