The photodegradation efficiency of o-chloroaniline (o-ClA) was studied in a dispersion of TiO2 with and without the use of iodate. Phosphor-coated mercury lamps that were emitting a wavelength of 300 nm, generating a total photon intensity of 5.6 x 10(-6) einstein L-1 s(-1), were used throughout the reaction. Decayed compounds o-chlorophenol and p-benzoquinone were identified as the major intermediates in the gas chromatography/mass spectroscopy (GC/MS) detection. The analysis was extended to total organic carbon (TOC) measurement and identification of end products, which have proven that UV/TiO2 is a clean process to mineralize aromatic organics into nontoxic CO2 and H2O. Further rate enhancement was examined by the selected oxyanion (IO3-) in the UV/TiO2. The use of IO3- generally improved the degradation; however, the performance was very much dependent on the system pH. The o-ClA decay was more favorable in acidic solution than in alkaline solution in UV/TiO2/IO3-. Such an effect could be justified by the IO3- reduction process and the generation of different radical species.