Chlorinated anilines are frequently used in the industry as starting materials for chemical synthesis. This type of compounds can end up as pollutants in wastewater. 2-Chloroaniline (2-ClA) was selected irradiating under monochromatic UV light at 300 nm. The reaction rate could be enhanced by introducing low level of H2O2 into the UV/TiO2 system. Excess H2O2 could not increase the HO center dot generation but retarded the reaction rate. The pH effect was also investigated in UV/TiO2 and UV/TiO2/H2O2 systems. All the experimental results show that pH is a sensitive parameter to the rate of degradation. Low reaction rate at acidic pH could be accounted by the dark adsorption test which has also proven the photocatalysis of TiO2 may contribute to a two-step process: (1) 2-ClA pre-adsorbed onto TiO2 and (2) photoexcitation of TiO2. At high pH, rate enhancement could be observed at UV/TiO2 system because of the increase generation of HO center dot. However, the introduction of H2O2 slowdown the decay rate at such alkaline medium. (c) 2006 Elsevier B.V. All rights reserved.