The photocatalytic oxidation of aqueous solutions of 2-mercaptobenzothiazole (MBT), 2-mercaptobenzinlidazole (MBI), 2-mercaptobenzoxazole (MBO), 2-mercaptopyridine (MP), para-tolylmercaptan (PTM) was investigated over a heterogeneous catalyst of TiO2, in a photocatalytic reactor. The effect of some physical and chemical parameters such as amount of catalyst, flow of oxygen, pH and time of irradiation were studied in order to optimise the process. These mercaptans are almost completely mineralised to carbon dioxide, ammonia and sulphate ion by photocatalytic method. The results obtained from photocatalytic oxidation of MBT have led us to propose a compound with the sum formula of benzothiazol-2-sulfonate (BTSO3) to be a main intermediate.