The effects of salinity on the photooxidative decolorization of rhodamine B in a variety of aqueous salt solutions were studied, aiming at the purification of seawater using a photocatalytic reaction. It was demonstrated that the photooxidative decolorization of rhodamine B in chloride salt solutions could proceed. It was found that the reaction was accelerated in the presence of a certain amount of salt and that a 2.0 wt% salt solution showed the fastest decolorization rate. Metal ions, Na+ and Mg2+, caused the enhancement of the photocatalytic activity at the same salt concentration as seawater. The reaction rate of photooxidative dye decolorization in seawater was slower than that in salt water although Na+ and Cl- are the major ions in seawater. (c) 2007 Elsevier B.V. All rights reserved.