Abstract: The competitive adsorption of arsenate and chromate was conducted on the surface of hydroxy-Fe-montmorillonite complex. The effect of the initial concentration and the addition order of arsenate and chromate on their uptake by hydroxy-Fe-montmorillonite complex was investigated. The results show that competitive adsorption does not exist between arsenate and chromate on hydroxy-Fe-montmorillonite complex under experimental conditions. The addition of the secondary anion increases the adsorption of the first one to some extent and this increase is proportional to the initial concentration of the two anions. The addition order of arsenate and chromate influences their uptakes to a certain extent, especially on the surface of hydroxy-Fe-montmorillonite complex. This phenomenon is more obvious for chromate for its relative weak affinity for adsorption on these surfaces.