Abstract: The decoloration of 7 anionic water-soluble azo dyes in aqueous solutions was carried out by using photo-assistant sodium bisulfite/ potassium borohydride system based reductant,and the reaction mechanism was analyzed through UVVis spectrum.The effect of concentration of reductant and irradiation strength on decoloration of dyes was investigated.In addition,rapid colorimetric determination of benzidine compounds released from(photo-)assistant reduction of selected direct dyes was also conducted.The results indicate that photo-assistant reduction of azo dyes may first lead to formation of hydride azo compounds,and higher concentration of the reductant and enhanced irradiation improve the decoloration of azo dyes.The confirmation of benzidine compounds in decolorized solutions demonstrates that further reduction of azo dyes with sodium bisulfite/ potassium borohydride system based reducing agent will produce aromatic amine.