Steel slag, commercial waste material containing silica and alumina which are the chemical components elements of zeolite, was used as a source for synthesis of FAU zeolite (Y-zeolite, X-zeolite). Through acid-treatment to remove CaO species from steel slag and hydrothermal treatment, well-crystallized Na type FAU zeolite was obtained. Furthermore the synthesized FAU zeolite was applied as a support of photocatalyst. It was found that hydrophobic surface property of zeolite enhances photocatalytic activity for decomposition of organic pollutants and the zeolite synthesized from steel slag would be applicable as promising support of TiO2 photocatalyst.