The TiO(2)-mediated photocatalysis process has been successfully applied to degradation of dye pollutants. Our results indicate that the TiO(2) surface is negatively charged, and the sulfan blue (SB) adsorbs onto the TiO(2) surface through the positive di-ethylamino groups while the TiO(2) surface is positively charged and the SB adsorbs onto the TiO(2) surface through the negative sulfonyl groups. In order to obtain a better understanding of the mechanistic details of this TiO(2)-assisted photodegradation of the SB dye with UV irradiation, five intermediates of the processes were separated, identified, and characterized by the HPLC-ESI-MS technique, which included a positive- and negative-ion mode. The results indicated that the N-de-ethylation process continues until the N-de-ethylated SB dye is completely formed. The probable photodegradation pathways were proposed and discussed. The reaction mechanisms of UV/TiO(2) proposed in this study should be useful for future applications of the technology to the decolorization of dyes.