Abstract: High concentration gaseous chlorobenzene was treated using ultraviolet(UV) radiation to evaluate the feasibility of UV technology as a pretreatment for biological removal of high concentration of halogenated volatile organics. The factors affecting the performance of the UV reactor, including UV wavelength, inlet mass concentration of chlorobenzene, empty bed retention time (EBRT) and relative humidity, were examined. The results indicated that single wavelength of254 nm showed no apparent removal of chlorobenzene while combination of 254 nm and 185 nm could demonstrate a good elimination capacity of chlorobenzene. Underthe condition of inlet mass concentration of 2 300～2 600 mg/m³ and EBRT of 27 s, about 40% of chlorobenzene was removed. Further increase of EBRT had little improvement in removal efficiency. Within the inlet mass concentration of more than 3　000 mg/m³, the chlorobenzene removal rate was less dependent on concentration, while showed an increasing relationship with the inlet mass concentration between the range of 150～3 000 mg/m³. Furthermore, the increase of relative humidity could enhance both removal efficiency and removal rate of chlorobenzene. The resultsdemonstrated a competitive potential as a pretreatment for high concentration of volatile organic compounds.